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This book has been prepared to meet the need in colleges 
for a text that would present the leading facts and theories 
in physiology in a concise yet adequate manner. There 
have been pubHshed several texts adapted to the needs of the 
medical student; and from the press have come many texts 
in physiology designed for the needs of the high-school 
student; heretofore no text written especially to meet college 
demands has been offered. The college student needs a 
text more dignified and serious than that suited to the ado- 
lescent mind of the high-school student; on the other hand, 
college requirements demand a less specialized text than that 
presumably needed by the technical student. Yet every 
college student ought to understand some of the funda- 
mental facts underlying the several activities of the human 
body, and these facts should be presented in a manner com- 
mensurate with his intellectual development; he is reaching 
forth for new valuable information, and the eagerness of 
his desire must be adequately met with suitable truth. It 
is confidently believed that this book will meet college needs. 

This text is well illustrated with anatomical pictures and 
physiological charts and diagrams. A detailed knowledge 
of anatomical structure is not essential for adequate under- 
standing of physiological activity, yet some idea of the 
machinery helps in appreciating the workings of the mechan- 
ism. The illustrations and diagrams may prove helpful in 


attaining a mental picture of the parts involved, and how 
they work. 

In high-school physiology texts some discussion of Hygiene 
is frequently added to each chapter; but Hygiene has now 
become such an important subject in itself that in most 
colleges a separate course is provided. It is far too important 
a subject to be discussed by sundry brief additions to chap- 
ters in a text-book of Physiology; moreover, physiology is 
more basic, and requires an entire semester for its own dis- 
cussion, so that there is no reason for the inclusion of Hygiene 
in a college text on Physiology. It may well be urged, how- 
ever, that the student should proceed to a study of Hygiene 
when he has completed the necessary preparatory work in 

Many important references to current periodical literature 
are given for the benefit of those who may wish to extend 
their information by consulting original sources. Advanced 
students will find additional helpful reading in standard 
texts on Physiology such as Starling, Howell, Schaeffer, 
Stewart, Burton-Opitz, and MacLeod; and in such texts on 
Biochemistry as Matthews, Robertson, and Hammarsten. 

A. D. B. 

Emory University, 



The Cell. 

Metabolism 18 

Irritability 19 

Motion 19 

Growth 19 

Reproduction 20 



Nutritive Condition 23 

Load 23 

Activity 23 

Rest 23 

Fatigue 23 

The Chemistry of Muscle 25 


Physiology of the Digestive System. 

Mastication 29 

Insalivation 31 

Ptyalin 32 

Deglutition 32 

Gastric Activity 34 

Origin of the Pepsin and Acid 39 

Secretion of Gastric Juice 39 

Absorption in the Stomach 40 

Intestinal Activity 40 

Digestion in the Small Intestines 41 

Intestinal Secretion 44 

Absorption in the Small Intestine 44 

Protein Absorption 44 

Carbohydrate Absorption 45 

Absorption of Fats 46 


Activity of the Large Intestine 46 

Digestion and Absorption in the Large Intestines ... 47 

Physiology of Organs Accessory to Digestion 48 

The Liver 48 

The PancJreas 52 

The Spleen 52 



The Amino Bodies 54 

The Carbohydrate History 57 

The Nutritive History of Fats 59 

The Inorganic Salts 61 

The Vitamins 62 

Accessory Articles of Diet 66 

Some Factors Affecting Metabolism 67 


Physiology of the Organs of Elimination. 

The Urine 69 

Constituents of the Urine 70 

Urea 72 

Purin Bodies 72 

Creatinin 73 

Creatin 73 

Hippuric Acid 73 

Inorganic Sulphates 73 

Ethereal Sulphates 73 

Sodium Chloride 74 

The Secretion of Urine 74 

Glomerulus 74 

Convoluted Tubules 74 


Physiology of the Heart. 

Course of Blood through the Heart 79 

Action of the Auricles 80 

Action of the Ventricles 80 

Time Relations of the Cardiac Cycle . 81 

Action of the Heart Valves 81 

The Heart Sounds 83 

Rate of the Heart-beat 84 

Force of the Heart's Action 86 


Intracardiac Pressure 87 

Changes in the Heart's Form and Position during Contraction . 88 

Properties of Heart Muscle 89 

Calcium, Potassium, and Sodium Action on the Heart . .90 

The Contraction Wave of the Heart ■ . 91 

Nutrition of the Heart 92 

The Cardiac Nerves 94 

Variation in the Electrical Condition of the Heart ..... 97 


Physiology of the Vascular System. 

Blood-pressure 99 

Variations in Blood-pressure 100 

The Pulse 102 

The Velocity of the Pulse Wave 102 

Interpretation of the Sphygmogram 103 

Venous Pulse 104 

The Vasomotor Nerves 104 

The Normal Regulation of the Vasomotor Apparatus . . . . 107 

Vasomotor Supply to the Different Regions 107 


Physiology or the Blood. 

Quantity 109 

Specific Gravity 109 

Constituents of the Blood 110 

Gases 110 

Proteins Ill 

Red Blood Corpuscles Ill 

Hemoglobin 112 

White Blood Corpuscles 113 

Blood Platelets " 113 

Coagulation of the Blood 113 

Immunity 115 

Physiology of the Lymph 116 


Physiology of the Respiratory System. 

Intrapulmonic and Intrathoracic Pressure Conditions .... 124 

Physical Changes in Respiration 125 

Chemical Changes in Respiration 125 

Condition of the Gases in the Blood 127 

Role of the Nitrogen 127 

Exchange of Gases in the Tissues 127 


Factors Affecting Respiratory Activity 129 

Breath Sounds 132 

Coughing 132 

Sneezing 132 

Hiccough 133 

Sobbing 133 

Snoring 133 

Sighing and Yawning 133 

Pleurae 133 

Artificial Respiration 133 


The Temperature of the Body and its Regulation. 

Heat Production in the Body 135 

The Loss of Heat from the Body 136 

Regulation of Heat Production 136 

Physiological Oxidations 137 

Regulation of Heat Loss 138 

The Nervous Control of the Heat Mechanism 139 


The Functions of the Skin. 

Heat Dissipation 141 

The Sense of Touch 142 

The Pain Sense 144 

The Temperature Sense 145 


The Nervous System. 

The Spinal Cord 157 

Functions of the Spinal Cord 158 

Conduction Functions of the Spinal Cord 163 

The Medulla and the Pons 167 

Motor Nuclei 175 

The Mesencephalon 180 

The Cerebellum 184 

Afferent Tracts 184 

Efferent Tracts 184 

The Diencephalon 186 



The Autonomic System. 

The Autonomic Response to Various Emotions 206 

Mesencephalic Group 206 

Medullary Group 206 

Thoracico-cervical Group 206 

Splanchnic Group 206 

Lumbar Group 206 

Sacral Group 206 

Gray Rami Distribution . 207 

Vomiting Center 207 

Heat Regulating Mechanism 207 

The Effect of Autonomic Afferents on Emotions and Mentality 207 

Spinal Centers of Reflexes 209 

Tendon Reflexes 210 

Cutaneous Reflexes 210 

Functions of the Cerebrum . . . .211 


Sleep. Dreams. Trance States. Emotions. 

Sleep 222 

Theory 1. Accumulation of Acid Waste Products . . . 222 

Theory 2. Accumulation of Sleep-producing Toxins . . . 223 

Theory 3. Anemia of the Brain 223 

Theory 4. Fatigue of the Vasomotor Center . . . . . 223 

Intensity of Sleep 224 

Dreams 224 

Trance States 226 

Emotions 227 


Special Senses. 

Hunger 229 

Appetite 230 

Sense of Thirst 230 

Sense of Taste 231 

Sense of Smell 232 

Limits of the Sense of Smell 233 



Auditory Sensations. 

The Limits of Hearing 245 

Projection of Auditory Sensations 246 

Semicircular Canals, tJtricle, and Sacculi 247 


The Physiology of Voice and Speech. 

The Voice 252 

The Pitch 253 

Timbre 254 

Speech 255 


Vision and Physiology of the Eye. 

Far Point of Distinct Vision 260 

Size of Image on the Retina 260 

Some Optical Defects of the Normal Eye . 261 

Chromatic Aberration 261 

Spherical Aberration 261 

The Iris 262 

Contraction of the Pupil . . . 262 

Dilatation of the Pupil 263 

Inherited or Acquired Optical Defects 264 

Myopia 264 

Hypermetropia 265 

Presbyopia 265 

Astigmatism 266 

The Retina and its Function 266 

Relation of the Stimulus to the Sensation 270 

Color Vision 271 

Color Blindness • • 276 

Test for Color Blindness 278 

Color Contrast 280 

Simultaneous • 280 

Successive Contrast 281 

Binocular Vision 281 

Visual Judgments 284 

Judgments of Size, Distance and Solidity 284 



Inteenal Secretions. 

Nutritional 288 

Protective , 295 

Parathyroids 296 

Morphogenetic 297 

The Thymus Gland 297 

The Thyroid Gland 297 

The Pituitary Body or Hypophysis 299 

Mammary Gland 300 

The Gonads 300 


The Physiology of Reproduction. 

Maturity 305 

Menstruation 305 

Ovulation , 306 

Maturation of the Ovum 306 

Nourishment of the Embryo 310 

Physiology of Parturition 313 

The Function of the Mammary Gland 314 

Secondary Sexual Characteristics 315 

The Determination of Sex ". . . .316 


Theories of Heredity 318 



Physiology is the study of the various functions of the 
hving organism, and of the conditions under which the 
several mechanisms normally operate. 

The subject might well be considered under two heads: 
Bio-physics, dealing with molar phenomena, and bio-chemics, 
dealing with molecular phenomena. The subject matter 
of this book is bio-physics, mainly, only such mention of 
the molecular phenomena being made as may be essential 
for more clearly explaining the main thought. 

It is customary and convenient to discuss the activities 
manifested by the living body according to the purposes a 
given aggregation of cell groups is assumed to subserve. So, 
somewhat arbitrarily, we subdivide the general activities of 
the body into the several activities of the anatomical groups, 
such as skeletal, digestive, circulatory, respiratory, etc. 
These several subdivisions refer more particularly to the 
specialized systems of the vertebrates, especially to the 
human form; but each of the several systems has a more-or- 
less definite prototype in forms way down the animal scale, 
forms out of which the human type seems to have evolved. 


The structural unit of the body is the cell (see Fig. 1). 
This unit manifests all those animal functions found in the 
highest type of animal, though of course these manifesta- 
tions here appear in their most protean form. These func- 
tions are: (1) Metabolism (comprising absorption, assimila- 
tion, utilization and elimination); (2) irritability, whereby 


the cell is susceptible to stimulation; (3) motion, whereby 
a response ensues to adequate stimulation; (4) growth, 
whereby a cell progresses from its earliest state, through 
maturity, to old age; (5) reproduction, whereby new cells, 
after its kind, are generated. 

^ j?^^"^ "^'=:^;:;; Pericellular surface. 

//'**" '^"\^_ Protective. 

^ 'X Fat body. 

^ ^^-^ \\ Nutritive. 

/ M^^^i ^^^ Nucleus. 

/ Ip'^^^^y ~~— -A— __ Telestic* 

/' W'^n2^^-~— -._ "^^"^ Nucleolus. 

// ^^x3^ ~~~- — ~~u~____^ Kinetic center for nucleus. 

/ \ Chromatin. 

/ ', Determinants for heredity. 

',' — — 1; Attraction sphere. 

II . ' - ,' Maturation kinetics. 

'1 © I f: Centrosome. 

,' ^ -; Activator for maturation. 

\ U Mitochondrium. 

\ . / Determinant for cell. 

^ — r Cytoplasm. 

\ / Metabolism material. 


Detritus (?). 



Fig. 1. — Diagram of a cell showing structural parts with the assumed func- 
tion of each part. 


In exercising this function the cell takes into its proto- 
plasm such food principles present in the enveloping medium 
as may be requisite for its general and special activity. 
These principles are the carbohydrates, proteins, fats, 
mineral salts, water, and oxygen, each in varying proportions 
to satisfy the particular requirements of the differing cell. 
From these the cell is able to synthesize material for the 
performance of its general functional activities, and also is 
able to sublimate portions for utilization in the nucleus in 
the preparation of a new cell entity. Whatever of the food 
principles taken into the general protoplasm of the cell is 
non-utilizable, or whatever becomes detritus in the attrition 
of the life process, is eliminated from the cell as waste. This 
continuous round of consumption and elimination is essential 
to the activity and life of the cell. 

* ( Telestic: involved more with the destiny of the cell than with its imme- 
diate metabolic activity.) 



Irritability is that property of a cell whereby it is suscep- 
tible to stimulation. Such stimulation may be derived from 
any external force impinging on the cell; in quality it may 
be neural, electrical, mechanical, thermal, or chemical. 
Different cells vary greatly in their relative susceptibility, 
some cells being highly irritable, while others are compari- 
tively indifferent. In the increasing differentiation of func- 
tion of the higher animals, certain cells become so specialized 
that they respond to particular kinds of stimuli only, as for 
example, the response of the retinal cells to the stimulus of 


Motion is that property of a cell whereby it responds to 
stimulation by some alteration of form, either of the whole 
cell or of some part. Such alteration of form of the whole 
cell is well illustrated by the amoeba; this movement may be 
in response to some attractive force, as when an amoeba 
surrounds and engulfs a particle of nutriment, or repulsive, 
as when an amoeba assumes the position of greatest resist- 
ance (the spheroidal) in response to some protopathic 
excitation; in the higher animals, the wandering white blood 
corpuscle exhibits amoeboid movements. Movements of 
parts of a cell are illustrated by the protoplastic streaming, 
whereby the contents of a cell slowly manifest alterations of 
position; and the ciliary movements, whereby the little hair- 
like processes projecting from the surface of a cell manifest 
a whipping motion; both kinds of motion are present in the 
higher forms. 


Growth is that property of a cell whereby it passes through 
the various stages of the life process from its first appearance 
as a definite entity, through immaturity, maturity, and old 


age. The higher the animal, and the more marked the various 
speciaHzations of function, the more differentiable become 
these several sequent stages. 


Reproduction is that property of a cell whereby new cells, 
possessing all the properties inherent to that kind of a cell, 
are produced from the original cell. The property of repro- 
duction seems to reside in the nucleus (Fig. 1) wherein are 
those determinants, the chromosomes, in which exist all the 
traits characteristic of that particular cell. Every indi- 
vidual of any form of life commences his life as a single cell 
from which is generated all the multiplicity of cells that make 
up the adult form. 

In unicellular organisms the specialization of function is 
often so obscure and protean as to escape detection except 
as manifested in final results. However, as the life process 
extends into the multicellular stage, this specialization of 
function becomes readily apparent as aggregations of cells 
become differentiated for specific purposes; some of these 
become specialized to give support and rigidity to the body, 
some to effect dynamic action, some to transmute external 
impressions into neural forces, others to manufacture chemical 
forces, and yet others to produce the species cells. But what- 
ever the specialized activity of these cell aggregates there 
continues for each the primary fundamental need for food 
and oxygen and for the removal of waste; to these ends are 
directed all the main activities of the organism, for only in 
this way can the organism continue its life and fulfil its 


From a physiological standpoint, as from a histological, 
muscle tissue is divided into three groups : Voluntary muscle, 
involuntary muscle, and cardiac muscle; voluntary muscle is 
also termed striated, since under the microscope numerous 
fine cross striations may always be discerned; involuntary 
muscle is also called smooth muscle, since it shows no cross 
striations; cardiac muscle is striped like voluntary muscle, 
but it also has branching communications unlike either 
striated or smooth muscle. As its name implies voluntary 
muscle is that muscle that can be contracted at will, though 
there are some instances of striated muscle, like the muscles 
that move the ear, that are beyond the control of the will 
with most people; for the most part, the voluntary muscles 
are attached at one or both ends to some bone or bones, and 
so are often called the skeletal muscles. Involuntary muscle 
is entirely beyond the control of the will; it is the contractile 
substance found associated within the walls of the hollow 
viscera of the body, the bloodvessels and other tubular 
structures, and about the hair follicles. Cardiac muscle, 
although striated, is probably never directly controllable 
by the will, though with some individuals its rhythm may 
be modified somewhat through the phrenic nerve (and so 
reflexly by way of the vagus nerve), or by simulated emo- 
tions; and this muscle is endowed with the remarkable 
property of rhythmic contractility. 

The specialized function of muscle is that of effecting a 
change of position of some integral part of the body. This 
function of muscle is exercised by virtue of the inherent 
quality of contractility, whereby a muscle when appropriately 
stimulated tends to lessen its longitudinal diameter and 


increase its lateral diameter (Fig. 2). When a contracting 
muscle is viewed under a microscope, and then compared 
with a muscle at rest, it is seen that each ultimate fibril of the 
muscle (termed a sarcostvle) has altered its shape from a 
cylindroid, when at rest, toward that of a spheroid, when 
stimulated. This contractile change whereby the sarcostvle, 
when stimulated, tends to assume the spheroidal shape may 
probably be considered a vastly specialized inheritance of 
that primitive response to stimuli whereby the unicellular 
amoeba when irritated instantly assumes the position of 
greatest resistance, i. e., the spheroidal. 

Fig. 2. — Diagram illustrating the change in form of a muscle (the biceps of 
the arm) when contracted. 

A muscle contracts normally whenever it receives ade- 
quate stimuli through its motor nerve from the central 
nervous system; or, in the case of the autonomic system, 
from the nearest ganglion in the direct reflex arc. Also it 
will contract whenever a suitable artificial stimulus, such as 
a mild electric current traverses its motor nerve. Moreover 
it will contract if adequate stimuli of various kinds (chemical, 
thermal, mechanical) are applied directly to the musple 
substance, thus indicating that a muscle possesses specific 

Under normal conditions the muscles of the body are in 
a »state of continuous though moderate elastic tension; 


assumedly this is due, for the most part, to a continual dis- 
charge into the muscle of subminimal nerve impulses coming 
from sundry sensory areas. This tonicity of muscle tissue 
tends to keep all intermediate joints in better apposition, 
and renders the response of the muscle to stimulation more 
prompt; it also, aided by the usual elastic balance between 
opposed flexors and extensors, abductors and adductors, 
renders all skeletal movement more smooth and precise. 
Many conditions modify the activity of muscle tissue: 

1. Nutritive Condition.— Muscle activity is depressed by 
loss of sleep, by hunger, worry, local anemia, extremes of 
heat or cold, or by the accumulation of toxins due to over- 
exertion, or by debility, local or general. Up to the optimum 
point, converse conditions tend to augment muscle activity. 

2. Load.— The activity of a muscle is influenced by the 
degree of load it is called upon to move; conditions otherwise 
being equal, the total amount of work possible to a muscle is 
greater when the load is small than when the load is large. 
That is, if the weight of the load be multiplied by the height 
to which the load is lifted, and the sum of all the products 
obtained in a given time be compared with a like sum where 
the load is considerably heavier, it will be found that the 
amount of work actually performed in this time will sum 
up more with the lighter load than with the heavier. 

3. Activity.— Activity in one set of muscles diminishes 
the amount of work simultaneously obtainable from another 
set of muscles. For example, one cannot lift so heavy a 
load with the muscles of the upper extremity if at the same 
time the muscles of the lower extremity are busily employed 
in producing a sharp thrust against some heavy object. 

4. Rest.— Intervals of rest between succeeding contrac- 
tions of a muscle postpone, or may even prevent, the onset 
of fatigue. 

5. Fatigue.— Complete fatigue of a muscle necessitates a 
succeeding prolonged interval of rest to insure complete 
recovery of normal power and activity. The normal minimal 
interval necessary for complete recovery from fatigue may 
be greatly extended by continued attempts to contract a 
completely fatigued muscle; therefore, the sensation of 



impending fatigue may wisely be considered a warning that 
further efforts be discontinued for a time. 

Fatigue has been well defined as a temporary loss of both 
irritability and contractility as a result of too long continu- 
ance of functional activity. The disappearance of irritability 
assumedly is due to an accumulation of katabolic toxins in 
the muscle substance, while the loss of contractility is con- 
sidered to be due to the temporary exhaustion of immediately 
available energy-producing material. The katabolic toxins 
are presumably lactic acid and carbon dioxide; and if these 
are not removed from the muscle as rapidly as they are 
formed in the process of contraction, then a benumbing 

Fig. 3. — Tracings on the kymograph showing gradual fatigue of a frog's 


action on susceptibility soon supervenes; inasmuch as the 
relative acidity of a muscle increases during repeated con- 
tractions, it is assumed that the katabolic toxins are not 
removed as rapidly as they are formed. The energy pro- 
ducing material is sugar from the blood that has been stored 
up in the muscle cells as muscle sugar; if muscle activity 
is not too strenuous the muscle cells apparently are able to 
pick up enough sugar from the circulating blood to compen- 
sate for the amounts being used; but if the muscle activity 
is excessive, then the consumption of sugar is in excess of 
the replenishment; consequently, the immediate store of 
energy yielding material becomes exhausted and the power 


of contractility becomes suspended until adequate replace- 
ment of sugar has taken place. 

Present experimental evidence indicates that all voluntary 
muscle contractions are the results of a fused series of rapid 
nerve impulses coming to the muscle at a rate varying from 
30 to 100 a second, the rate depending much on the particular 
muscle involved, and somewhat on the temperament of the 


The chemistry of muscle is too wide a subject to be intro- 
duced here, but brief reference may be made to such of it as 
pertains to the phenomena of contraction. 

As indicated above, muscle tissue has the power of taking 
up the monosaccharid, dextrose, and converting it into a 
polysaccharid called muscle glycogen. This muscle sugar 
forms from 0.5 per cent to 0.9 per cent of the weight of the 
well-nourished resting muscle, but this ratio steadily dimin- 
ishes when the muscle is in a state of activity. 

It is believed that the glycogen is split into a simpler body 
or bodies by means of the energy arising from impulses from 
the nervous system; and it is thought by some that the 
first decomposition product from the glycogen is lactic acid, 
inasmuch as this acid always appears as an accompaniment 
of muscle activity. The acid seems to be immediately oxi- 
dized to carbon dioxide and water, with the liberation of 
much heat. (One chemical formula for sugar is C6H12O6; if 
this were converted into lactic acid there would result the 
formula (€311603)2; if this was then oxidized by the addition 
of twelve parts of oxygen, there would result 6CO2+6H2O.) 

If the sequence of chemical changes taking place in the 
muscle on contraction is similar to that expressed in the 
formula of changes from sugar through lactic acid to carbon 
dioxide and water, as stated above, then a molecular theory 
might be advanced for explaining the physics of contraction. 
In place of 1 molecule of sugar within a given area there 
would be produced 6 molecules of carbon dioxide and 6 mole- 
cules of water, that is, 12 molecules in place of 1. It has 


been shown by van't Hoff that the law of Avagadro (''Equal 
volumes of gases, with the same pressure and temperature, 
contain an equal number of molecules") is measurably true 
of solutions; it follows, then, that if the number of molecules 
in a given area be increased there will follow an increase of 
molecular pressure within that area; also, if that increase of 
pressure is accompanied by the evolution of heat, the mole- 
cular pressure will be augmented in direct ratio. If such an 
increase of molecular pressure occurs within an elastic 
cylindroid container, the shape of the container will change 
from a cylindroid to a spheroid; its long diameter will be 
diminished, and its cross diameter will be increased. The 
ultimate sarcostyle of the muscle is such a cylindroid con- 
tainer; in muscle contraction, there is an alteration of the 
cylindroid toward that of a spheroid; sugar disappears from 
the muscle, lactic acid accumulates if the supply of oxygen 
is inadequate, carbon dioxide and water are produced, and 
much oxygen is used up with a concomitant evolution of 
heat. The theory seems to be consistent with the phenomena. 
The promptly succeeding relaxation is due to the extremely 
rapid diffusion of the water and of the carbon dioxide, espe- 
cially the latter. 

Another theory advanced to account for the mechanics of 
contraction is that the changes in diameters is due to altera- 
tions of surface tension from the sudden presence of acid 
products following excitation. However, Bernstein contends 
that the amount of work produced in a given contraction is 
much greater than can possibly be accounted for by surface 

Another explanation that has been proposed is the imbibi- 
tion theory. This theory assumes an explosive endosmosis, 
brought on by the excitatory liberation of acid molecules 
within the sarcoplasm, with a resultant swelling producing 
shortening; while the subsequent relaxation is due to the 
removal of the acid products through diffusion, oxidation, 
or resynthesis. From the viewpoint of the mechanics 
involved this theory seems improbable inasmuch an effective 
imbibition could hardly take place with any such lightning- 
like rapidity. 


The amount of work done by a contracting muscle can 
be computed by multiplying the weight of the load by the 
height to which the load is lifted; then the heat equivalent 
may be obtained by making use of the formula : One calorie 
is equal to 426.5 grammeters of work. For example: If in 
unit time a muscle lifts 42.65 gm. to the height of 10 meters, 
then it has done an amount of work equivalent to 1 calorie. 
Experiments performed by Zuntz, in which the energy 
changes were computed from the oxygen absorbed and the 
carbon dioxide eliminated, show that the energy obtainable 
in work from a given intake of food material varies from 25 
per cent in the arms to about 40 per cent in the legs; he also 
found that the efficiency, as indicated by this mechanical 
equivalent, may be increased by suitable training. 

Plain or unstriated muscle tissue differs functionally from 
striated tissue in: (1) Relative . sluggishness of movement; 
(2) capability of remaining in a state of contraction for long 
periods of time; (3) the power occasionally shown of rhyth- 
mic contractility, especially in the ureters and alimentary 

The peculiar contractility characteristic of smooth muscle 
is manifested in the following locations: (1) Digestive tract 
in: (a) the muscularis mucosae from the esophagus to the 
anus; {h) the muscular coat of the alimentary tract from the 
lower half of the esophagus to the anus; (c) the excretory 
ducts of the salivary glands, liver, gall-bladder, and pancreas. 
(2) Respiratory tract: The posterior part of the trachea, and 
the circular bundles of the bronchi. (3) Urinary tract: In 
the pelvis and capsule of the kidneys, in the ureters, bladder, 
and urethra. (4) Female generative tract: In the broad and 
round ligaments, vagina, uterus, oviducts, and in the erectile 
tissues of the nipples, clitoris, and labyrinthi vulvae. (5) 
Male generative tract: In the epididymis, vas deferens, seminal 
vesicles, prostate body, and the Cowper glands. (6) Lymph- 
atic system: In the trabeculae and capsule of the spleen, and 
in some of the larger lymphatic nodes. (7) The vascular 
system: In the coats of arteries, veins, and larger lymphatics. 
(8) The skin: In the sweat glands, some sebaceous glands, 
in the muscles that erect the hairs, and in the skin of the 


genitals. (9) The eye: In the iris and cihary muscles, and 
in the eyelids. 

Cardiac muscle tissue has a response intermediate in 
speed between plain and striated muscle, but possesses the 
remarkable property of continued rhythmic contractility. 

Cells possessing motile cilia seem to have retained the 
flagellate power of earlier primitive cell types. This kind of 
activity proceeds from the cell, and is apparently indepen- 
dent of the nervous system. Little is known of the nature of 
the dynamic impulse producing the lashing of cilise. 


Lee, et al.: General Properties of Muscle, Am. Jour. Phys., 1916, 40, 446. 

Harris: Time Relations of the Voluntary Contractions in Man, Jour. 
Phys., 1894, 17, 315. 

Hill: Mechanical Efficiency, Jour. Phys. 1913, 46, 435. 

Mackenzie, W. C: The Action of Muscles, 1918. 

Hill: Muscular Activity and Carbohydrate Metabolism, Science, 1924, 
60, 1562, 505. 


The digestive system (Fig. 4) is associated with the ali- 
mentary tract, extending from the mouth to the anal outlet. 
It comprises the mouth, in which take place the processes 
of mastication and insalivation; the esophagus, a tube for 
conveying the food from the mouth to the stomach: the 
stomach, in which occur the earlier stages of protein diges- 
tion; the duodenum, into which are poured the digestive 
juices coming from the liver and pancreas; and the small and 
large intestines, in which organs processes of digestion and 
absorption continue. 

Mastication.— Mastication is a process of cutting and of 
grinding. The cutting process, which is for the purpose of 
obtaining fragments of convenient size for chewing, is well 
performed by the eight incisor teeth. The incisors normally 
meet with a scissors action, the under set passing slightly 
to the rear of the upper set. Under more primitive conditions 
than now the strong canine teeth were useful for rending and 
tearing the more resistant portions of food. The molar 
teeth serve as grinders to further reduce the food to much 
smaller subdivisions, and so prepare it for a more rapid 
reduction by the various digestive juices. 

Biting is usually performed by moving the lower jaw, or 
mandible, in a vertical plane upward, by means of the tem- 
poral and masseter muscles; but the grinding movements 
involve a slight lateral movement at the end of the vertical 
motion; this lateral movement is performed by the pterygoid 
muscles; the lateral movement becomes more apparent 
when hard coarse foods, like nuts, are being eaten. During 
the process of chewing, the tongue keeps the mass moving 
about the mouth, placing and replacing the larger fragments 




Cavity of mouth 

Opening of larynx 

Transverse colon (cut) 

Hepatic flexure of colon 

Common orifice of bile and 
pancreatic ducts 

Pancreatic duct 

Splenic flexure of colon 

Fig. 4. — General view of the digestive system (diagrammatic). The 
transverse colon has been cut to show the duodenum, but its course is indi- 
cated by dotted lines. The vermiform appendix is seen hanging down from 
the cecum. The loop of large intestine which precedes the rectum is marked 
"sigmoid flexure," and includes the iliac colon and the greater part of the 
pelvic colon. (Cunningham.) 



between the teeth until all portions are reduced to a size and 
consistency suitable for swallowing. At the same time, the 
muscles of the cheek keep the food from escaping beyond the 
teeth on their outer borders. 

The eruption of the teeth is shown in this table : 

Lower central incisors 
Upper incisors . 
Lateral incisors . 
Canines . 
First premolars . 
Second premolars 
First molars . 
Second molars . 
Third molars » . 

Milk teeth. 
6 to 9 months 
8 to 10 months 
12 to 21 months 
16 to 20 months 
15 to 20 months 
20 to 24 months 

Permanent teeth. 

7th year 

7th year 

8th year 

11th to 12th year 

9th year 

10th year 

6th year 

12th to 14th year 

17th to 25th year 

Insalivation.— Insalivation is the process of incorporating 
the food in the mouth with the saliva. The saliva comes 
from three sets of glands, the parotids, the submaxillary, 
and the sublingual. From the parotid glands comes a saliva 
intimately concerned with the digestion of cooked starch; 
from the submaxillary and sublingual glands comes a saliva 
relatively rich in mucin; so the parotid secretion serves more 
in dissolving soluble parts of food and in acting on cooked 
starch, while the secretion from the other glands assists more 
in lubricating the food so it can be swallowed readily. 

The secretion of saliva is excited by the presence in the 
mouth of sapid substances, by the thought or smell of savory 
food, and also by chemical and mechanical stimuli. Dry 
solid food induces a much larger flow than does wet food; 
furthermore, it is claimed by Pawlow, dry foods only are 
capable of exciting secretion from the parotid gland ; whereas 
meats, acids, and even the sight of food, stimulates secretion 
from the submaxillary gland. The flow of saliva is, therefore, 
a reflex phenomenon; the neural center controlling salivation 
is assumed to be in the medulla near the nuclei of origin of 
the glosso-pharyngeal nerve. 

Saliva has several functions to perform. As a liquid it 
dissolves the soluble constituents of food making them appre- 
ciable to the sense of taste, and making them more readily 
susceptible to the digestive action of the contained enzyme. 


It changes the food to a consistency more suitable for swal- 
lowing; by means of the mucin present it lubricates the food 
for more easy passage through the pharynx and esophagus; 
and by means of its particular enzyme, ptyalin, it chemically 
modifies some of the starch constituents of the food. 

Ptyalin.— Ptyalin is an enzyme that converts cooked 
starch into maltose and dextrin by the process of hydrolytic 
cleavage, ^. e., by incorporating into the starch molecule one 
molecule of water. This action takes place in a mildly 
alkaline or neutral solution, as weak an acidity as 0.003 per 
cent serving to entirely inhibit the action of ptyalin. Yet 
salivary digestion may continue for a considerable period 
after the food has been swallowed, inasmuch as acidification 
of the food by the gastric juice takes place somewhat slowly 
and from the surface of the mass toward its center; so in the 
meanwhile ptyalin digestion may continue within the depths 
of the food mass. 

Deglutition.— When the mouthful of food has been suffi- 
ciently moistened and comminuted, the tongue gathers it 
into a bolus and conveys it, by a gliding pressure against 
the palate, to the isthmus of the throat at which place and 
moment the bolus is shot into the lower rear part of the 
pharynx by a sharp contraction of the muscles (mylohyoid) 
of the floor of the mouth (Fig. 5). This contraction of the 
mylohyoid muscle, with the assistance of others, serves to 
pull the opening into the larynx up under the base of the 
tongue and so largely prevents food from entering the respir- 
atory tract at this point. Also during the passage of the 
food through the pharynx the nasal cavity is shut off by a 
contraction of those palate muscles that draw the soft palate 
upward and backward. 

As soon as the bolus of food strikes the back portion of the 
pharynx a wave of contraction starts in the pharyngeal wall 
at a point just above, and quickly forces the food into the 
esophagus and there initiates a series of peristaltic contrac- 
tions that force the bolus of food on down into the stomach. 
If the food be sufficiently liquid, it can descend through the 
esophagus by gravity mainly, though aided somewhat by 
the impetus given it by the muscles of the mouth. If the 



food is semi-solid, however, it is carried through the esophagus 
by a succession of peristaltic muscle waves. The time occu- 
pied by the bolus of food in traversing the esophagus and 
entering the stomach, after a brief delay at the cardiac 
orifice, is about six seconds. 

Fig. 5. — Position of the tongue in the first movement of deglutition. 

The peristaltic movements in the esophagus are not trans- 
mitted by the excitation of contiguity but by a segmental 
series of neural reflexes. This reflex has its initiatory impulse 
started in the region of the pharynx whence it sets up a series 
of segmental reflexes in the esophagus, each segment con- 
tracting in due season and in a manner quite independent 



of the immediately preceding contraction as the original 
pharyngeal stimulation suffices for the induction of each, 
and all, of the succeeding series. 


The stomach is a hollow container having elastic contrac- 
tile walls which adapt it to holding widely varying quantities 
of food. As a result its cavity is never any larger normally 
than it is made by the contained food (Figs. 6 and 7) pressing 

A B 

EiG. 6. — A, Diagram showing shape and position of moderately filled 
stomach. Erect posture. B, Diagram showing shape and position of dis- 
tended stomach. Erect posture. (Hertz.) 

against the inner wall; when no food is present, the anterior 
and posterior walls are in apposition. The first food taken 
occupies the place of digestive advantage in direct contact 
with the gastric mucosa; succeeding ingesta lodge within 
the preceding material (Fig. 8). 

Within a few minutes after food enters the stomach, peri- 
staltic waves of contraction start in the middle region and 
run at intervals of about twenty seconds toward the pylorus 
(Fig. 9). These contraction waves serve to mix the food 
thoroughly in the right half of the stomach and to press it 
up into the pylorus for timely ejectment into the duodenum. 

Incisura cardiaca 

Antrum cardiacum 

Gastric canal 
Incisura angularis 

Duodenum _ , . .-i. 7 

Pyloric antrum Pyloric vestibule 

Sulcus intermedius 

Fig. 7. — Diagram showing the subdivisions of the human stomach. 
(F. T. Lewis.) 

Fig. 8. — Stratification in the stomach of succeeding ingesta of food. 

Fig. 9. — Peristaltic contraction waves in the stomach. 


Closure of the sphincter between the pylorus and duodenum, 
with continued peristaltic waves in the antrum yylori, results 
in a spurting back of the chyme centrally into the food mass 
in the body of the stomach, thus serving to more intimately 
mix the materials with the gastric juice and thus facilitate 
gastric digestion. 

The movements of the stomach are automatic, that is the 
impulses are derived from reflexes operating through the 
intrinsic nerve ganglia; yet, though these movements are 
automatic, they may be greatly influenced, both favorably 
and unfavorably, by impulses coming from the central" 
nervous system. Impulses coming through the vagus nerve 
tend to augment the vigor of gastric muscle activity, while 
those coming though the sympathetic group of nerves tend 
to depress this activity. Generally speaking, any condition 
that promotes the comfort and well-being of the body as a 
whole aids the normal peristaltic activity of the stomach; 
whereas any condition that depresses or interferes with the 
comfort and well-being of the body, or arouses emotions 
antagonistic to such comfort and well-being, will serve to 
inhibit partially or completely, the stomach movements. 

The mechanism acting on the pyloric sphincter has not 
yet been completely determined. However, it is known that 
consistency of food is one important factor; liquid food 
induces early relaxation of the sphincter, while solid parts in 
the food tend to prevent this relaxation. A more effective 
factor seems to be the relative acidity of the gastric contents, 
as the sphincter tends to open more readily when the chyme 
becomes increasingly acid; yet this factor is somewhat modi- 
fied by the nature of the food material inasmuch as carbo- 
hydrate material when alone passes through the pyloric 
orifice early, even before becoming markedly acid. Some 
recent roentgen-ray observations of the stomach, made by 
Carlson, indicate that the pyloric sphincter may relax 
rhythmically at the termination of a series of six to eight 
contraction waves running up the antrum. Probably there 
are other factors not yet discovered. 

Closure of the sphincter seems to be due to a reflex originat- 
ing in the duodenum as a result of the action on the acid 



chyme on the duodenal mucosa (Fig. 10); and it is claimed 
that the sphincter will not again normally relax until this 
acidity in the duodenum has been neutralized. This arrange- 
ment may be looked upon as a protective mechanism to 
prevent flooding of the duodenum with an acid mass since 
an excess of acid material would markedly interfere with 
duodenal digestion. 

In the pyloric portion of the stomach (Fig. 11), is secreted 
that portion of the gastric juice having specific digestive 
action on protein foods. Human gastric juice is a thin color- 
less secretion having a specific gravity of about 1.002, and 
an acidity at the height of digestion of about 0.4 per cent. 
It contains small amounts of mucin, protein, and inorganic 


Sensory Neurone 

Mucosa of 

Motor Neurone 


Fig. 10. — Diagram illustrating mechanism of control of pyloric sphincter. 

salts; but its most important constituents are its digestive 
enzymes, pepsin and rennin, and its hydrochloric acid. 

Pepsin is a proteolytic enzyme of unknown chemical com- 
position. It manifests its digestive activity when in an acid 
medium only. It acts on proteins by a process of hydrolytic 
cleavage whereby it converts the proteins, after they have 
been acidified, first into primary proteoses, then into second- 
ary proteoses, then into peptones; this last product, peptone, 
is much unlike protein in that it is freely soluble in water, 
and is not coagulable by heat. Besides the three stages 
mentioned, of the conversion of protein into peptone, there 
are probably considerable numbers of intermediate stages 
each of which represents a probable reduction in the size 
and complexity of the protein molecule. 


Not all of the protein in food is reached and acted upon 
by the gastric juice. Experimental examinations made of 
the chyme as it was injected into the duodenum showed 
that as much as 20 per cent of the protein was undigested. 
It would seem that much of the pepsin action is preparatory 
for the further proteolysis which occurs in the small intestine; 



Plexus of Meissncr 
Muscularis mucosae 
Sensory neurone 

Fig. 11. — Diagram illustrating how the extrinsic nerves to the intestine 
communicate with the intrinsic ganglia controlling intestinal activity. 

in fact, some proteins, such as serum albumin, seem not to 
be reducible by the proteolytic enzyme of the pancreas until 
they have first been acted upon by pepsin. 

Milk in the stomach is first acted upon by a coagulant 
to which has been given the name of rennin. It is assumed 
that the subsequent reduction of the protein in the milk, 


casein, is thereby facilitated; moreover the early coagulation 
of this constituent of milk prevents its otherwise early 
escape into the duodenum, and the casein, thus separated 
from the whey, is in a favorable condition for pepsin action. 
Starchy material is not digested in the stomach, but the 
action of ptyalin on the starchy material may continue until 
stopped by the acid of the gastric juice. Fats are liquefied 
by the warmth of the stomach, and partially emulsified by 
the churning to which the chyme is subjected, but the diges- 
tion of fats probably does not take place at all in the stomach. 
Collagen is converted into gelatin peptones; mucin is changed 
into bodies allied to glycosamine; nucleo-proteins are in part 
converted into proteoses and peptones, while the nucleins 
are precipitated but not digested. 

Origin of the Pepsin and Acid.— The exact origin of the 
pepsin and acid is not conclusively known. Pepsin is thought 
to be formed as a propepsin in the central cells of the gastric 
tubules and becomes active as pepsin when secreted and 
brought into contact with the acid. The acid is thought to 
originate in the parietal cells of the tubules as a neutral 
chloride of an organic base, but this does not become an 
active acid until it reaches the mouth of the gland. It is 
not known what it is that converts the neutral chloride into 
hydrochloric acid, or how this change is effected. The 
source of the chlorine in the hydrochloric acid is assumed to 
be the sodium chloride of the blood and tissues, but what 
may be the intermediate transmutation is as yet unknown. 

Secretion of Gastric Juice.— The secretion of gastric juice 
is stimulated in several ways. (1) There is what is known 
as the psychic secretion whereby the increased formation 
of gastric juice is stimulated through pleasurable sensations 
of taste and smell, or even by pleasurable memories of such 
sensations; these sensations or emotions induce impulses that 
travel to the secretory area of the stomach by w^ay of the 
vagus nerve. (2) Certain substances such as meat juices 
and meat extracts contain hypothetical principles termed 
secretogogues; these secretogogues, when they are released 
by partial digestion from the foods containing them, serve 
to excite the glandular parts of the stomach; they are abun- 


dantly present in meats, are absent in bread and white of 
egg, and are present in milk in but a limited degree. (3) 
Proteins of all kinds, when partially digested in the stomach, 
seem to release or develop substances which act on the gastric 
mucosa, especially upon that of the pyloric region, so that a 
new substance termed secretin is formed; this secretin does 
not act upon the glands of the stomach directly, but is 
absorbed into the blood and carried by the blood stream to 
the gastric glands and there excites these glands to renewed 
activity; such a substance thus acting is termed a hormone. 

The quality and digestive power of the gastric juice varies 
with the nature of the food; it usually is maximal with those 
types of food normally subject to peptic activity, but in 
some cases may be more active with food of less permeability. 

Absorption in the Stomach.— Absorption in the stomach 
takes place to a variable degree. Fats are not absorbed at 
all; sugars seem to be absorbed somewhat, the amount of 
absorption depending somewhat on the relative concentra- 
tion; it is doubtful, however if the stomach can absorb any 
but the monosaccharids. Formerly it was stated that some 
absorption of protein material took place in the stomach, 
but more recent observations indicate that all of the protein 
intake can be recovered from a postpyloric fistula; this 
indicates that probably no protein is absorbed from the 
stomach wall. Water seems not to be absorbed at all, but 
passes promptly into the duodenum; it may be, however, 
that very warm water has a slight permeability. Present 
experimentation indicates that the various salts are absorbed 
slowly or not at all; but the observations on this point are 
not conclusive. The extent to which drugs may be absorbed 
in the stomach has not been satisfactorily determined. 


The small intestines normally exhibit two kind of major 
activity. The first consists of rhythmic segmental contrac- 
tions incited apparently by the presence of food within the 
canal; in this type of activity a definite area of the bowel 


suddenly becomes temporarily constricted in several rings 
within a restricted zone, thereby breaking up the column of 
food into a number of segments; this process is repeated at 
different rings in the same segment, thus further dividing 
the separated pieces into smaller lots; these contractions 
proceed at an estimated rate of about thirty a minute; 
eventually the several subdivisions are caught up and swept 
along as a whole for renewed segmentations further on. 
The sweeping along of the contents of the bowel constitutes 
the second type of activity; it is termed peristalsis. This 
peristaltic movement is wave-like in form, and consists of a 
moving contraction that proceeds along the intestinal wall 
an indefinite distance, pushing ahead of it the contents of the 
bowel in that area. Each such wave of peristaltic contraction 
is immediately preceded by a definite wave of rapid relaxa- 
tion, and is succeeded by an area of less extensive and slow 
relaxation. Under normal conditions this peristaltic wave 
always proceeds from the stomach downward and is the main 
agent for producing the onward passage of the intestinal 
contents. The speed of this progression is such that about 
four hours is required, on the average, for material to pass 
from its entrance into the duodenum to the ilio-cecal valve 
where the small intestine empties into the large bowel. Thus 
the first material to pass through the pyloric opening has 
reached the large intestine before the stomach has entirely 
emptied itself of its contents. 

Like the movements in the stomach the intestinal move- 
ments are automatic, being controlled by the intrinsic ganglia 
and connections; but like similar activity in the musculature 
of the stomach, the intestinal activity may be both favorably 
and unfavorably influenced by impulses coming from the 
central nervous system. Most of the impulses augmenting 
the intestinal activity come to the bowel by way of the vagus; 
practically all the extrinsic inhibitory impulses come to the 
bowel by way of the sympathetic fibers. 

Digestion in the Small Intestines.— Digestion in the small 
intestine is effected by the enzymes contained in the secretion 
poured in from the pancreas, assisted considerably by the 
bile (from the liver) and by the secretion from the duodenal 



mucosa. These digestive elements will be considered in 

The secretion from the pancreas (Fig. 12) is a thin limpid 
liquid, alkaline in reaction, and with a specific gravity of 
1.0075. It contains three important enzymes: Trypsin (or 
Protease), which is proteolytic in action; Amylase , which is 
an enzyme acting on carbohydrates; and Lipase, which acts 

Fig. 12. — The duodenum and pancreas. (Gray.) 

on fats. The amount of secretion has been observed in 1 
case to vary from 500 cc. to 800 cc. in a day, the quantity 
depending somewhat on the character of food taken; after 
a meal of bread alone there is a more abundant secretion 
than after a meal of meat alone, though this results in part 
from the earlier ejection of the carbohydrates from the 
stomach. Again the particular enzyme seems to vary in 


amount with the demand, each increasing in amount with a 
corresponding increase in the food of its particular congener. 

The secretion of pancreatic juice begins as soon as the 
first material is poured into the duodenum from the stomach. 
Experimental work by Starling seems to indicate that as 
soon as the acid gastric juice comes into contact with the 
duodenal mucosa a special substance or hormone, termed 
duodenal secretin, is developed; this secretin is taken up by 
the blood and carried to the pancreas which it stimulates to 
functional activity. The pancreas then pours forth a copious 
watery secretion which increases to its maximum quantity 
in about three hours. The trypsin in this secretion is inactive 
as it qomes from the pancreas, and remains so until it comes 
into contact with the duodenal mucosa, whereupon it is con- 
verted from the inactive form, called trypsinogen, to the 
active form, known as trypsin, the activating substance in 
the bowel producing this conversion is known as enterokinase. 
The other pancreatic enzymes are probably active when 

Trypsin acts upon the proteins by a process of hydro- 
lytic cleavage; this action proceeds most advantageously 
in a mildly alkaline medium though it can continue in a 
neutral or in a mildly acid medium. The action of trypsin 
is far more rapid and complete than is that of pepsin, though 
it seems to act best when preceded by pepsin. Trypsin con- 
verts proteins into proteoses, these into peptones, and these 
into a great number of substances of smaller molecular 
weight none of which give the biuret reaction characteristic 
of proteins. These reduced substances are grouped under 
the general heading of amino-acids; some of these are mon- 
amino-acids, like leucin, tyrosin, and glycin; others, like 
lysin, arginin, and histidin, are diamino-acids ; yet another 
group, which is neither protein nor amino-acid, is termed the 
polypeptids. These final products of tryptic digestion repre- 
sent a reduction of the protein foods to a condition suitable 
for absorption into the intestinal bloodvessels. 

Amylase acts by hydrolyzing starches, either cooked or 
uncooked, and converting them into maltose and achro- 


Lipase acts by hydrolyzing neutral fats and breaking them 
up into glycerin and the constituent fatty acid. The fatty 
acids thus released combine with alkali salts, present in the 
food and in the bile, to form soaps; these soaps mingle with 
the liquid fats forming a fine emulsion which in turn is more 
readily attacked by the lipase. Besides this main action, 
lipase seems to have a reversible action also, synthesizing 
the fatty acids and glycerin into fats and then breaking these 
fats back into glycerin and fatty acid. The reducing action 
of the lipase on fats is greatly facilitated by the presence of 
bile; in this facilitation, the bile is assumed to have an energiz- 
ing effect on some lipase that is relatively inactive; it may be, 
too, that the bile salts have a solvent effect on the fatty 

Intestinal Secretion.— The intestinal secretion, sometimes 
called the succus entericus, is derived from the glands lining 
the intestinal wall, especially of the duodenum. In this 
secretion, besides the enterokinase mentioned, there are 
found three other enzyme groups : Erepsin, some invertases, 
and nuclease, Erepsin hydrolyzes peptones and deutero- 
albumoses, thus supplementing the action of trypsin. It is 
assumed that nuclease is effective in digesting the resistant 
nucleins. The inverting enzymes are: M alias e, which con- 
verts maltose and dextrin into dextrose; invertase, which 
converts can sugar into dextrose and levulose; and lactase, 
which converts milk sugar into dextrose and galactose. 
The significance of these inverting enzymes acting as they 
do to change disaccharids into monosaccharids, is found in 
the interesting fact that polysaccharids are not utilizable by 
the tissues of the body. 

Absorption in the Small Intestine.— About 85 per cent of the 
products of intestinal digestion are absorbed by the villi of 
the small intestine. It is believed that absorption is chiefly by 
a selective activity of the cells of the intestinal walls, aided 
to a variable extent by the mechanical forces of diffusion 
and osmosis. 

Protein ^fe^orpifzW.- Experimental evidence indicates that 
proteins are absorbed as salts of amino-acids by the blood- 
vessels of the intestinal villi (Fig. 13). These salts are in 



part modified by the liver for excretion, but for the most 
part are rapidly removed from the blood by the tissues of the 
body in which tissues they are utilized for specific metabolic 
requirements and replacement. 

Thoracic Duct 
Avenue for Fats 


Fig. 13. — Avenues of absorption. 

Carbohydrate Absorption.— \]Y\[e^^ taken in excess, prob- 
ably the greater part of the sugars and starches consumed 
are converted into dextrose in the small intestine, then 
absorbed through the bloodvessels of the villi, and thence 
carried by the portal vein to the liver. In the liver all 
dextrose in excess of 0.15 per cent is withdrawn from the 
blood stream and stored up as glycogen; the balance circu- 
lates in the blood to be taken up by the tissues for specific 
metabolic purposes. Too large an amount of dextrose in the 
blood stream overtaxes the glycogenic powers of the liver, 


and this results in an excess of sugar free in the blood; such 
a condition throws on the kidneys the added work of elimi- 
nating the excess, and there appears sugar in the urine as a 
result; such an end-result is known as alimentary glycosuria. 
Carbohydrates that escape absorption from the small intes- 
tine usually undergo bacterial fermentation wdth the result 
that there are produced acetic, butyric, and succinic acids, 
carbon dioxide and hydrogen. 

Absorption of Fats.— Tresent evidence indicates that 
absorption of fats takes place somewhat as follows: The 
fat having been split into fatty acids and glycerin, and the 
fatty acids having been dissolved in solutions of bile salts, 
the epithelial cells of the villi pick up these constituents of 
fat, pass them through the stroma of the villi, and recombine 
them by means of a tissue enzyme into a fat of extremely fine 
emulsion; then the fat is taken up by the lacteals and con- 
veyed through the thoracic duct to the left subclavian vein 
where it is poured into the blood stream. After a meal con- 
taining fats, the lacteals of the mesentery are filled with a 
milky chyle that discloses a fat emulsion when examined 
under the microscope. A small amount of fat is probably 
taken up by the mesenteric bloodvessels and carried to the 
liver. Absorption is more rapid and complete with fluid 
fats like olive oil than with solid fats like that from mutton. 
Absorption diminishes rapidly with decrease of bile in the 


The investigations of Cannon indicate that the bowel 
contents are retained in the cecum and ascending colon for 
about two hours by means of a frequent reverse peristalsis 
whereby the semi-liquid material is forced back again and 
again into the cecum from the ascending colon; the delay 
retention of the material in this region permits of more exten- 
sive absorption, especially of the water and dissolved salts. 
From the hepatic flexure of the colon the bowel contents are 
forced onward by a series of contraction waves running 
toward the rectum^ several of which may be occurring simul- 


taneously within a limited area. Gradually in this way the 
digestive residue is worked eaudad into the sigmoid flexure 
and rectum. 

It is probable that the entrance of this residue into the 
rectum normally initiates the impulse to defecation; though 
not infrequently, especially with females, the rectum may 
become loaded with residue without producing any aware- 
ness of the fact. Pressure of the accumulating residue 
against the internal sphincter of the anal canal induces a 
relaxation of this muscle, after which voluntary control of 
the external sphincter alone can delay the completion of 
defecation. Usually the abdominal muscles, by increasing 
intra-abdominal pressure, assist in the expulsion of the rectal 
contents, the levator ani muscle and both sphincters being 
relaxed meanwhile. 

The peristaltic waves in the large intestine, as in the small 
intestine, are determined by the intrinsic nerves and ganglia 
which control the musculature; but the extrinsic nerves may 
effect many modifications of these movements, sometimes 
accelerating the movements and sometimes inhibiting. 

Digestion and Absorption in the Large Intestines.— So far 
as is known there are no digestive enzymes secreted by the 
large intestine or into it, but for a considerable period the 
enzymes brought along with the material from the small 
intestine continue their hydrolytic cleavages. Absorption 
also continues, especially of the waters, salts, and other 
soluble principles, but it is very doubtful if fat absorption 
takes place beyond the ileo-cecal valve. A marked charac- 
teristic of the large bowel is its property of absorbing water, 
particularly in the cecum, ascending and transverse colons; 
by this water extraction, the semi-liquid material from the 
small intestine becomes solidified to the normal formed 

After birth a large and varied number of bacteria are always 
present in the alimentary canal. In the small intestine these 
bacteria are principally concerned with the splitting of some 
of the carbohydrates into lactic and acetic acids; in the large 
intestine other bacteria cause a putrefactive decomposition 
of the protein molecule into a great number of simpler bodies 
such as indol, skatol, phenol, fatty acids, carbon dioxide, 


hydrogen sulphide, and so on. Whether or not any of these 
decomposition products are utiHzable by the body does not 
yet appear; some observers contend that absorption of these 
products is distinctly deleterious to health. They seem to 
be absorbed to some extent, and may be identified in the 
urine; when absorbed, they first undergo an oxidation and 
become united to sulphur to form an ethereal acid compound 
called a ''conjugated sulphate;" thus the phenol unites to 
form a phenolsulphonic acid salt, indol becomes an indoxyl- 
sulphonic acid salt, and skatol unites in a similar way. Undue 
absorption of these products undoubtedly throws a needless 
strain upon the eliminative organs, even if the general organ- 
ism may have acquired an adaptive resistance to the toxic 
properties. It is contended that limiting the protein intake 
to somewhere near the bodily requirements greatly dimin- 
ishes the probability of excessive intestinal putrefaction. 

The feces represent the undigested and undigestible 
residues of the food; along with these residues there will be 
various decomposition products, secretions, excretions, 
bacteria, bile products, mucus, gases, water, and inorganic 
salts. The color of normal feces is brown, and is due to the 
presence of bile pigment. The odor is due to the skatol, 
indol, fatty acids, and hydrogen sulphide. The average 
amount in twenty-four hours is approximately 200 gm.; this 
relative amount is increased by a preponderating vegetable 
diet and decreased when meat foods preponderate. 


The Liver (Fig. 14).— The liver has three well-known func- 
tions to perform, namely: the production of bile, the synthesis 
of glycogen, and the formation of urea. It also possesses 
some less well-understood functions having some relation to 
the development of fibrinogen and to the development of 

Bile is a thin, yellowish-green, alkaline fluid of a specific 
gravity of 1.020; it is secreted continuously by the liver 
cells, the daily output amounting to about 600 cc. on the 
average. However, it is only during digestion that the bile is 



poured out into the duodenum; in the interims it accumulates 
in the gall-bladder. The presence of acid chyme in the duo- 
denum reflexly excites a contraction of the gall-bladder and a 
synchronous inhibition of the sphincter of the gall duct at 
its point of entrance into the duodenum (Fig. 15). Each 
increment of chyme, therefore, is accompanied by an inflow 
of bile. Also, there seems to be an increased production of 
bile during digestion, possibly as the result of some hormone 

ductus venosus 

Papillary Fossa for umbilical vein 

Fig. 14. — Posterior and inferior surfaces of the liver. (From model by His.) 

The more important constituents of bile are the bile salts, 
the bile pigments, and cholesterol. The bile salts, sodium 
glycocholate and sodium taurocholate, are formed in the 
liver cells probably from some protein substance in the blood. 
These salts serve to maintain the cholesterol in solution; 
they are of great service in the splitting of fats in the small 
intestine; they assist in neutralizing the acid chyme, and in 
precipitating the contained proteins; a portion is reabsorbed 



from the intestines and again excreted by the liver whose 
activity it seems to stimulate. 

The bile pigments bilirubin and biliverdin are disintegra- 
tion products of hemoglobin; in this disintegration of hemo- 
globin the hematin component passes away in the bile 
pigments while the greater part of the iron component is 

Circular Muscle /^^^^ 
of Gall Bladder 

Impulse of Stimulation 

of Bile Duct 


Impulse of Inhibitition 

Duodenal Mucosa 

Fig. 15. 

■Diagram illustrating a reflex control of the gall-bladder and the 
bile duct. 

retained in the liver for future syntheses. Some of the pig- 
ment is reabsorbed from the bowel and appears in the urine, 
but the greater part is eliminated through the bowel contents 
as stercobilin. 

Cholesterol is a product collected by the blood from the 
tissue cells of the body, and later removed from the blood 
by the liver cells. It may be considered a product of kata- 


bolism excreted by the liver for elimination from the body 
through the bowels. 

The functions of the bile may be summarized as follows: 
(1) It aids lipase in the digestion of fats; (2) it exerts a 
favoring influence on the digestion of proteins; (3) it serves 
as a vehicle for the elimination from the blood stream of 
some products of katabolism. 

Glycogen is derived chiefly from the dextrose in the portal 
vein by a process of dehydration; another source of glycogen 
is the non-nitrogenous portion of the amino-acid bodies; a 
further source is from the glycerin constituent of fats espe- 
cially the reserve fats of the body. 

The most generally accepted theory as to the function of 
glycogen is that it is a reserve supply of carbohydrate mate- 
rial, accumulated from the excess present during the active 
period of digestion, and gradually released for utilization 
during the interim between meals. The amount of sugar 
normally present in the blood is about 0.15 per cent; the 
storage in the liver of the excess present during digestion, 
and its gradual release later, serves to maintain the mean 
supply in the blood. The glycogen stored in the liver is 
reconverted to blood sugar by means of a specific diastasic 
enzyme normal to the liver; the stimulation to activity of 
this enzyme producing glycogenolysis may possibly be due 
to a relative reduction of the sugar tension in the blood. 

The ultimate utility of the glycogen is to furnish a source 
of chemical energy to the tissues, especially to the muscle 
tissues. The gradually released dextrose is carried by the 
blood stream to the muscle and other tissues and there 
taken up and held as temporary reserve in the form of tissue 
glycogen. As mentioned under the discussion of contrac- 
tility, this dextrose in muscle tissue is oxidized into simpler 
elements with an explosive release of energy whenever the 
necessary stimulus appears. Consumption of the dextrose 
is for a time compensated by a release of the accumulated 
muscle glycogen, and later by a release from the store of 
liver glycogen. Excessive activity soon creates an urgent 
demand for new carbohydrate material to renew the supply 
of essential sugars to the energy-consuming tissues. 


Urea is the principal nitrogenous end-product of protein 
metabolism. From the tissues it arises as a waste product 
which is gathered up by the blood in the form of carbonate 
of ammonia which is carried to the liver there to be dehy- 
drated into urea. Also, from some of the mon-amino prod- 
ucts of digestion, the NH4 group is split off as an ammonia 
compound to be later converted into urea by the liver. Urea 
may likewise be split off directly from some of the diamino 
bodies, like guanidin, for example. Thus the liver serves 
to convert the waste products of tissue activity, and the 
superfluous products of protein decomposition, into innocu- 
ous forms ready for elimination by the kidneys. 

When the tissues have worn out the reparative material 
furnished by the protein-amin supply, the waste product 
is cast forth into the blood stream and appears in the urine 
as creatinin. 

The Pancreas (Fig. 12).— There has been previous discus- 
sion of the digestive functions of the pancreas resulting from 
the secretion of the three enzymes, trypsin, amylase, and 
lipase. But the pancreas possesses an internal secretion, 
also, one that has a profound influence on the metabolism 
of sugars. This secretion is produced by little groups of 
cells called the islands of Langerhans; these cell groups are 
not connected in any way with the pancreatic duct which 
conveys the digestive enzyme to the duodenum, but each 
group is surrounded by a network of capillaries from which 
they obtain the constituents out of which they elaborate 
an internal secretion and into which they pour the secretion 
when formed. As will be shown later, in Chapters IV and 
XX, this secretion has an important bearing on the assimila- 
tion of sugar by the tissues. 

The Spleen.— Very little is known about the physiological 
significance of the spleen; a few facts have been gathered, 
however, that help a little toward an understanding of its 
mystery. It is known that during digestion the spleen 
slowly enlarges, reaching a maximum in about four hours, 
then slowly contracts; but just what is the significance of this 
swing is unknown. It is known also, that in cats and dogs 
at least, there is a rhythmical contraction and relaxation 


of the spleen occurring at intervals of about one minute; 
this seems to result in the maintenance of a steady vascular 
condition, but just what end is thereby subserved is problem- 
atical. There is evidence that the spleen takes iron from dis- 
integrated red blood cells; possibly it utilizes this metal in 
the formation of new corpuscles, a function possessed by the 
spleen in fetal life. Total extirpation of the spleen is not 
followed by constant or untoward results. 


Cannon: Mechanical Factors in Digestion. 

Pawlow: Work of the Digestive Glands. 

Bayliss: Nature of Enzyme Action. 

Bean: The Eruption of the Permanent Teeth, Am. Jour. Anat,, 1914, 
vol. 17. 

Stiles: Rhythmic Activity of the Esophagus, Am. Jour. Phys., 1901, 5, 

Cannon: Nature of Gastric Peristalsis, Am. Jour. Phys., 1911, 29, 250. 

Rogers: Reflex Control of Gastric Vagus Tone, Am. Jour. Phys., 1917, 
42, 605. 

Mall: A Study of the Structural Unit of the Liver, Am. Jour. Anat., 1906, 
vol. 5. 

Alvarez: Rhythm of Segments from Different Parts of the Intestine, 
Am. Jour. Phys., 1915, 37, 267. 

Cannon: Innervation of the Intestine, Am. Jour. Phys., 1906, 17, 429. 

Bradley: Lipase Reactions, Jour. Phys. Chem., 1910, 8, 251. 

Carlson, et al.: Character of Saliva and Blood Supply, Am. Jour. Phys., 
1907, 20, 180. 

Carlson: Secretion of Gastric Juice in Man, Am. Jour. Phys., 1915, 37, 50. 

Chittenden, Mendel and Jackson: Protein Digestion as Affected by 
Alcohol, Am. Jour. Phys., 1898, 1, 164. 

Chittenden and Albro: Influence of Bile Salts of Proteolysis, Am. Jour. 
Phys., 1898, p. 307. 

Langworthy and Holmes: Digestibility of Foods, U. S. Dept. Agric. Bull., 
1917, p. 505. 

Herter and Kendall: Influence of Diet on Intestinal Flora, Jour. Biol. 
Chem., 1909, 6, 499 and 7, 203. 

Bloor: Absorption of Fat, Jour. Biol. Chem., 1915, 23, 317. 

Folin and Denis: Absorption of Proteins, Jour. Biol. Chem., 1913, 14, 

Reid: Absorption of Sugars, Jour. Phys., 1901, 26, 427. 

Baldwin, W. M.: The Pancreatic Ducts in Man, Anat. Record, 1911, 
vol. 5. 



Examinations of subjects living on various diets, from 
that of semi-starvation to one that is replete, have shown 
that in a state of health there exists a nearly perfect balance 
between the nitrogen taken in with the food and that passed 
out in the waste of the body. This balance is spoken of as 
the nitrogen equilibrium. It rises and falls in direct ratio 
to the nitrogenous material consumed, but remains constant 
under constant conditions. Inasmuch as the presence of 
nitrogen in either the food intake or in the w^aste excreted is 
indicative of the presence of the protein molecule, estimations 
of protein units are regularly made by establishing the quan- 
titative nitrogen identity and multiplying the result by the 
proportionate factor (6.25) of nitrogen present in the protein 


The amino bodies in the portal system, representing the 
protein constituents of food material, serve two important 
purposes. A part of the amino substances is probably 
selected by cells needing nitrogenous substances for resyn- 
thesis into reconstructive material. Since the activity of 
any cell involves wear and destruction of material, there 
must be a constant call from the cells of the body for repara- 
tive substances; and inasmuch as protein is the only sub- 
stance containing all the constituents essential to protoplasm, 
it follows that without a continual supply of new protein, 
the cells will promptly succumb to katabolic detrition. Pro- 
tein, then, is furnished to the cells by the amino bodies, each 
tissue cell apparently having the faculty for selecting those 
particular constituents peculiar to its own molecular consti- 

The amount of protein material needed for the repair 
of tissue wear, or for the purposes of growth, is relatively 


indeterminate; but in all probability far greater amounts 
are normally consumed than are actually needed, except in 
those diets where the protein element has been cut down 
to the so-called irreducible minimum. The balance of the 
protein ingested is apparently deamidized in the liver; the 
split off ammonia portion is converted into urea and then 
excreted by the kidneys, while the remainder of the molecule, 
the organic acid radicle, may become synthesized into sugar 
and so become available as a source of energy. This explana- 
tion is largely hypothetical at present but experimental 
evidence makes it seem probable. 

It becomes then an interesting problem to determine how 
much protein is necessary daily to maintain the nitrogenous 
needs of the body. The average diet among civilized people 
shows for adults a daily ingestion of protein of about 120 
gm., about 90 per cent of which is absorbed and assumedly 
utilized; this amounts to about 1.5 gm. of protein for each 
kilogram of body weight as the daily average consumption 
of nitrogenous material. However, a prolonged series of 
experiments by Chittenden indicate that the body may be 
maintained in a state of normal efficiency if the ingestion of 
protein amounts to only 0.75 gm. per kilo body weight; but 
this does not necessarily prove that the lesser amount will 
continually yield optimum results. Yet it may be that 
0.75 gm. protein per kilo body weight is adequate for main- 
taining a nitrogen balance that does not interfere with either 
comfort or efficiency, and that this amount really represents 
the average daily wear and tear from cellular metabolism; 
in other words, that this amount completely satisfies daily 
cellular needs. If this conclusion be correct, then the excess 
protein ordinarily consumed is either wasted, or else is 
utilized as a source of energy more economically supplied 
by the carbohydrates and fats, or else becomes an extra 
burden on the organs of elimination. 

The amount of protein required varies somewhat with the 
age and sex of the individual, his occupation, and his tempera- 
ment. According to Starling the growing boy between the 
ages of fourteen and nineteen years, because of accelerated 
metabolism require more protein relatively than does the 


adult man; and the girl between the ages of eleven and sixteen 
years requires more relatively than does the woman aged 
thirty years, but the female of any age does not require as 
much as the male of the same age. A manual laborer requires 
more absolutely, but not relatively, than does the man of 
sedentary occupation simply because of his greater cellular 
katabolism; but the excess in energy requirements by the 
manual laborer is largely met by increased consumption of 
carbohydrates and fats. The individual with a minimum 
length of bowel, the so-called carnivorous ty^e, will require 
more protein relatively, under uniform conditions, than will 
the so-called herbivorous type who usually possesses a bowel 
longer than the average. 

There exist considerable differences as to the nutritive 
availability of the several proteins used as food. As a general 
thing the animal proteins are more readily and completely 
digested than are proteins from the vegetable kingdom. 
Experiments by Osborne and Mendal show^ that such pro- 
teins as the casein of milk, and the vitellin of egg, each con- 
tain all the nitrogenous material necessary for the mainte- 
nance of growth; that the leguminous proteins are adequate 
for maintenance but not for growth; and that some of the 
alcohol-soluble proteins from wheat, rye, and barley are 
inadequate for growth because they lack the amino-acid, 
lysin. Gelatin lacks three important amino-acids: trypto- 
phan, tyrosin, and cystein. The protein of Indian corn 
lacks tryptophan, lysin, and glycin. Proteins that thus lack 
important amino-acids are inadequate for the repair of 
tissue; a diet restricted to such proteins will result in bodily 
debility; but if the missing amins be added to the diet by 
giving supplementary articles containing such amins, then 
the diet becomes adequate for both maintenance and growth. 

The main facts of protein metabolism are summed up in 
the following table: 

Protein plus Pepsin equals Proteose. 

Proteose plus Trji^sin equals Amino-acids a and h. 

Amino-acid a plus an X enzjTne equals Urea and an organic acid. 

Organic acid plus ? equals Utilizable sugar. 

Amino-acid h plus ? equals an amin body. 

Amin body plus a Y enzjone equals Cell protein. 

Cell protein plus a Z enzyme equals Creatinin. 

Creatinin is a waste product and is excreted through the kidneys. 



As previously stated, the carbohydrates found in the portal 
vein, as absorbed from the small intestine, consist chiefly 
of dextrose; small amounts of both galactose and levulose 
are also probably present. These pass to the liver where, 
except in time of excessive carbohydrate ingestion, they are 
at once converted to gycogen and stored up as such in the 
liver cells. To the supply thus obtained will be added what- 
ever pro-sugar substance may be derived from the deamid- 
ized protein molecule and from fat. 

The supply of sugar in the circulating blood is kept fairly 
constant; this constancy is maintained by a continuing 
glycogenolysis from the liver, so adapted in amount as to 
meet the tissue needs of the body. The principal tissue 
using sugar is muscle. The sugar brought by the blood 
stream as dextrose is again converted into a glycogenoid 
substance termed muscle-sugar, in which form it is tempor- 
arily stored in the muscle for later dynamic uses. The next 
steps in the utilization of sugar are uncertain; but, from 
chemical data, the assumption is made that the resynthe- 
sized dextrose is metabolized through several possible inter- 
mediate stages into lactic acid, and ultimately into carbon 
dioxide and water. This change, glycolysis, always accom- 
panies muscle activity, of which it may be the dynamic 
factor; during the latter part of this process a great amount 
of heat is produced, in fact, the principal heat formation in 
the body, and the maintenance of body temperature, is 
effected by the oxidations occurring in muscle tissue. The 
carbon dioxide hereby formed passes into the blood, by 
means of relative gas pressure, and is conveyed to the lungs 
for removal from the body. The water formed may be 
partially utilized by the muscle plasma, but the larger part 
is carried off by the blood stream for elimination by the 
lungs, skin, and kidneys. 

Regulation of the supply of sugar at various points within 
the body is very complex. The conversion of sugar into 
glycogen, called glycogenesis, is under one control; the reverse 
process, the reconversion of glycogen into blood sugar, glyco- 


genolysis, is under another control; the consumption of 
blood sugar by the tissues, glycophysis, is under special 
control; while the utilization of the sugar for dynamic pur- 
poses, glycolysis, is controlled by yet another means; but all of 
them are intimately correlated in action, so that if one con- 
trol becomes perverted the entire organism may be badly 
deranged. A closely related condition is h^^^erglycemia, in 
which there is a more abundant supply of sugar in the portal 
vein than the liver is able to convert into glycogen; as a result 
the relative content in the blood stream rises above the crit- 
ical point, and sugar escapes through the kidney epithelium 
and appears in the urine; ordinarily this is a temporary con- 
dition due to an abnormal ingestion of sugars. Sugar appears 
in the urine as a regular phenomenon in the disease known 
as diabetes, but this results from the excess in the blood when 
the tissues lose much of their ability to take up the form of 
sugar available. Clinicians have lately discovered the reverse 
condition in which there is a diminished quantity of available 
sugar present in the blood; this condition might be due to 
inadequate glycogenolysis, or to greatly heightened glyco- 
physis; it has also been noted in the treatment of diabetes 
by insulin when too large a dosage of the pancreatic extract 
had been administered. 

The exact nature of the controls over sugar metamorphosis 
in the body is imperfectly understood. The process of gly co- 
genesis is probably primarily that of selective cellular 
activity, aided by a special enzyme; it is affected by any 
condition that modifies the relative vitality of the liver cells 
intimately concerned. Glycogenolysis is produced by a 
special hepatic enzyme whose activity is probably controlled 
by the relative sugar tension in the blood, and perhaps by 
the products of muscle activity; moreover, it is modified 
by the pressor action of the secretion from the adrenals, 
more obscurely by the secretion from the h3T)ophysis, and 
rather profoundly by the extrinsic nerve action. Glyco- 
physis, it may be assumed, is primarily under the influence 
of the relative glycic pressure in the blood and muscle plasma; 
but it is chiefly controlled, both in extent and quality, by the 
secretion, termed insulin, from the islands of Langerhans 


in the pancreas; this action of insulin is presumably to so 
modify blood sugar as to make it readily acceptable to the 
tissue cells. The control of glycolysis is even more obscure; 
apparently it is largely under the influence of those nerve 
impulses that eventuate in muscle action. 

Besides furnishing a source of energy directly to the tissues, 
and developing heat through its oxidations, sugar serves in a 
way to protect the proteins of the body, inasmuch as in its 
absence or deficient suppl}^ the body proteins or the proteins 
in the food are called upon to furnish the essential quota of 
energy-producing material. \ further use of sugar in the 
blood is in the manufacture by synthesis of a carbohydrate 
fat; this is a process demonstrable by biological experiment, 
but not duplicable at present in the laboratory of chemistry. 

The principal facts of carbohydrate metabolism are 
summed up in the following table: 

Carbohydrates plus Ptyalin results in Disaccharids. 

Disaccharids plus Amylase results in Monosaccharids. 

Monosaccharids plus Liver enzyme o results in Glycogen. 

Glycogen plus Liver enzyme h results in Blood sugar. 

Blood sugar plus Pancreas hormone results in an X sugar. 

This X sugar plus X-ase results in Muscle sugar. 

Muscle sugar plus Neural impulse results in Lactic acid. 

Lactic acid plus ? ? ? results in an intermediate. 

Intermediate plus Oxygen results in CO2 and H2O. 


The fat absorbed from the small intestine by the lacteals 
is conveyed through the thoracic duct to the left subclavicular 
vein and there emptied into the blood stream. By the blood 
it is slowly distributed to all the tissues of the body; it enters 
into the protoplasm of each cell; it is stored up in the alveolar 
tissues of the body as a reserve supply of readily-available 
combustible material; it is deposited around organs and 
serves as a cushion and means of protection; it is deposited 
in the subcutaneous areas of the body and there serves as 
insulating material against the too rapid dissipation of body 
heat; in this area it also serves esthetic ends; probably much 
of it ultimately becomes a source of heat and energy. 


From chemical data it is believed that the final products 
of combustion of fats within the body are carbon dioxide 
and water, but where and how this takes place in the body 
is not known. Certain deductions drawn from the metabolic 
abnormalities evoked by the disease of diabetes point rather 
inconclusively to the following hypothesis : When the supply 
of liver glycogen is inadequate to meet the dynamic needs of 
the body, through some means some of the storage fat is 
reconverted into a fat suitable for circulation in the blood; 
this blood fat is carried to the liver and there reduced by 
several steps into a pro-substance out of which blood sugar 
can be manufactured; the blood sugar thus made is then 
carried to the muscle tissues and there serves as a source of 
heat and energy in the same way as sugar from some other 

It is said that the body fat found in the carnivora, and 
possibly in the carnivorous type of humans, is derived largely 
from the fatty foods in the diet ; while the fat found in herbi- 
vora, and possibly in the herbivorous ■ type among humans, 
is derived from the carbohydrates in the food by a process 
of synthesis from the sugars. 

Fat forms an important element of all nerve cells; it enters 
into the composition of the protoplasm of all living cells, 
and is apparently essential to the life of the cell, but just what 
specific function it subserves in the cell is not determined. 

Fat is an excellent non-conductor of heat, and thus serves, 
especially in the colder climates, an important purpose in 
the retention of the heat of the body. 

The main facts concerning the metabolism of fat are 
summarized in the following table: 


plus Bile 

equals Emulsified fats. 

Emulsified fats 

plus Pancreas lipase 

equals Glycerin and fatty 

Glycerin, f. acids 

plus Intestine lipase 

equals Blood fat a. 

Blood fat a 

plus Tissue lipase 

equals Body fat. 

Blood fat a 

plus Tissue enzyme 

equals Protoplasm fat. 

Body fat 

plus Tissue lipase 

equals Blood fat h. 

Blood fat h 

plus Liver enzyme X 

equals Utilizable sugar. 

Protoplasm fat 

plus Service 

equals Lecithin. 

Lecithin is a waste product and is excreted in the bile. 



Besides those foodstuffs that supply reconstructive 
material, or heat, or energy, there are other substances that 
are vital to the welfare of the body. Within the body are 
found the chlorides, carbonates, sulphates, phosphates and 
fluorides, of sodium, potassium, calcium, iron, and magne- 
sium, as well as some organic iodine found in the thyroid 
tissue. These salts are widely distributed, some being found 
in the blood, some in the tissue, and nearly four-fifths of the 
total in the bones; the total mineral matter in the body con- 
stitutes about 4.3 per cent of the total weight of the body. 

Though these salts possess no known nutritive properties 
they have some exceedingly important functions to perform 
in the animal economy. Iron is essential for the transmission 
of oxygen to the tissues ; it exists in the blood as a constituent 
of hemoglobin. Calcium, sodium, and potassium are of 
extreme importance in relation to the irritability of nerve 
and muscle, especially to the activity of heart muscle; calcium 
increases the irritability of heart muscle, while sodium and 
potassium decrease its irritability. Calcium is extensively 
utilized in the building of bone; it is an essential factor in 
producing coagulation of blood ; it frequently becomes unduly 
increased in amount in the walls of bloodvessels in old age. 
Sodium, in the form of sodium chloride is apparently the 
chief salt used for maintaining the osmotic relationship in 
the tissues and liquids of the body; on this physical process 
depends largely the interchange of nutrient constituents 
throughout the body; the tissues are especially retentive of 
the sodium salt, maintaining enough for normal isotonicity 
even when there is serious deprivation of supply. These 
several salts are found in all protoplasm, and seem essential 
to the normal reactions of the living cell. They are likewise 
essential to the aggregate of cells, for if animals be fed on a 
mineral-free diet they soon succumb. Iodine is essential to 
the normal condition and growth of bone and connective 



Numerous experiments and observations indicate that 
connected with the foodstuffs are elements having profound 
influences on bodily mechanism. Fowl fed on polished rice 
soon develop a polyneuritis to which they rapidly succumb; 
yet during their illness they may be brought back quickly to 
health if to their diet of polished rice there be added some of 
the rice polishings, or some flesh food. If young rats be fed 
on purified casein, plus all other elements of an ordinary 
diet, they will cease to grow and will soon die, though they 
may be saved if to their trial diet there be added some whole 
milk or some purified butter. In the Orient many people 
living too exclusively on a rice diet suffer from a disease 
called beriberi characterized by paralyses and contractures; 
but their disease rapidly lessens and finally disappears if to 
the patients are given small quantities of rice polishings, in 
fact the disease is cured if even extracts of the rice polishings 
are given the patients. The extract made from these polish- 
ings resembles in chemical structure some of the compounds 
of nucleic acid; they may have an important function in 
connection with the metabolism of cells especially nerve 
cells. However, the amin component does not seem essential 
for the curative effect observed inasmuch as substances 
derived from fats appear to have the same restorative effect 
in some cases. The original name assigned to these substances 
is vitamins; but when it was found that their presence was 
best made known by their action, and when also it was 
found that the nitrogen component was not essential, some 
general classifying names were assigned them. One that was 
found most frequently in butter fat was called "Fat-soluble 
A;" another that was found often in the leaves of vegetables 
was designated "Water-soluble Bf' a third, first found in the 
juice of oranges and lemons was called just Vitamin C. 

On experimentation it was found that an animal deprived 
of foods containing the fat-soluble A soon developed a con- 
dition known as rickets; the addition of butter fat to the 
deficient diet soon cured the rickets; and children suffering 
from rickets improved remarkably when given a balanced 


diet in which butter fat was an essential component. If an 
animal were fed on a diet in which there was a deficiency of the 
water-soluble B it soon developed an inflammation of the 
peripheral nerves, akin to that manifested in the disease 
beriberi; the addition to the diet of foods containing the 
vitamin soon corrected the condition; and people afflicted 
with the disease of beriberi are relieved by the administration 
of those foods that are known to be rich in this vitamin. A 
similar history pertains to vitamin C which prevents scurvy, 
or which cures it when present; when this vitamin is absent 
from the diet, scurvy is very apt to be present. It seems 
highly essential then that a diet be so arranged as to have in 
it these three important vitamins, in addition to the requisite 
amounts of proteins, carbohydrates, and fats. 

The appended table, (p. 64), taken from the Journal of the 
American Medical Association, indicates the proportionate 
value of different articles of food in relation to the presence of 
the several vitamin factors. A single cross indicates that factor 
is present; two crosses indicate that the factor is present in 
considerable amount, relatively; three crosses indicates that 
the food so listed is relatively rich in that particular vitamin. 

Some recent experiments by Steenbock indicate that olive 
oil can be made as effective as cod-liver oil for anti-rachitic 
purposes by exposing it for one-half hour to the irradiation 
of ultra-violet light. 

Another factor in food has been discovered, the absence of 
which interferes with the procreative ability; this factor has 
been designated the X-vitamin. It is present in abundance 
in wheat embryo, in the seeds of corn, oats, cotton, lettuce and 
alfalfa; and in the green leaves of plants, lettuce especially. 
It is present in milk fat, egg yolk, walnut oil, and banana. 
It is low in most vegetable oils, is almost lacking in cod-liver 
oil and in potatoes. 

Fat-soluble A ' 

Water-soluble B 

Classes of Foodstuff. 

or anti-rachi 


or anti-neuritic 





butic factor. 

Fats and Oils: 


+ + + 


+ + 

Cod-liver oil . 

+ + + 

Mutton fat .... 

+ + 

Beef fat or suet . 

+ + 

Peanut oil 


Fish oil, whale oil, etc. . 

+ + 

Margarin prepared from 

animal fat ... . 

Value in 
portion ' 



Nut butters .... 


Meat, Fish, etc.: 

Lean meat (beef, mutton, 





Liver . 

+ + 

+ + 



+ + 


Heart . 

+ + 


Brain . 


+ + 



+ + 

Fish, white 

Very slight, if 


Fish, fat (salmon, her- 

ring, etc.) .... 

+ + 

Very slight, if 

Fish, roe 


+ + 

Canned meats 


Very slight 

Milk, Cheese, etc.: 

Milk, cow's whole, raw . 

+ + 



Milk, skim, raw . 



Milk, dried whole 

Less than + -f 


Less than -{- 

Milk, boiled, whole 



Less than -f- 

Milk, condensed, sweet- 




Less than + 

Cheese, whole milk 




+ + 

+ + + 



+ + 

+ + + 


Cereals, Pulses, etc.: 

Wheat, maize, rice, whole 




Wheat germ .... 

+ + 

+ + + 

Wheat, maize, bran . 

+ + 

Linseed, millet 


+ + 

Dried peas, lentils, etc. . 

+ + 

Soy beans, haricot beans 


+ + 

Germinated pulses or 



+ + 

+ + 




Fat-soluble A 

Water-soluble B 

Classes of foodstuff. 

or anti-rachitic 

or anti-neuritic 




butic factor. 

Vegetables and Fruits: 

Cabbage, fresh (raw) 

+ + 


+ + + 

Cabbage, fresh (cooked) 



Cabbage, dried 



Very slight 

Cabbage, canned . 

Very slight 

Swede (rutabaga) raw ex- 

pressed juice 

+ + + 


+ + 


Spinach (dried) 

+ + 


Carrots, fresh raw 




Carrots, dried 

Very slight 

Beetroot, raw, expressed 


Less than -\- 

Potatoes, raw .... 



Potatoes, cooked . 


Beans, fresh, scarlet run- 

ners, raw .... 

+ + 

Onions, cooked 

+ at least 

Lemon juice, fresh 

+ + + 

Lemon juice, preserved . 

+ + 

Linie juice, fresh . 

+ + 

Lime juice, preserved 

Very slight 

Orange juice, fresh 

+ + + 

Raspberries .... 

+ + 






Very slight 

Tomatoes (canned) . 

+ + 



+ + 


Yeast, dried .... 

+ + + 

Yeast, extract and auto- 



+ + + 

Malt extract .... 

-|- in some 

None of the three factors were found in : 


Olive, cottonseed, cocoanut or linseed oils. 

Cocoa butter. 

Hardened fats, animal or vegetable in origin. 

Margarin from vegetable fats or lard. 

Cheese from skim milk. 

Polished rice, white wheaten flour, pure cornflour, etc. 

Custard powders, egg substitutes, prepared from cereal products. 

Peaflour (kilned). 

Meat extract. 





These consist of certain flavors and spices added to foods 
to increase the general attractiveness and palatabiHty of the 
diet; also certain beverages taken for the pleasantness of 
their flavor as well as for the systematic reaction produced. 


Fig. 16 

The flavors, especially the aromatic ones, assist in digestion 
through the stimulating efl'ect they produce reflexly on the 
gastric secretion (page 39), soups and meat extracts also 
stimulate the gastric glands both reflexly, and directly 
through their possession of secretogogues of the second class. 
The beverages consist of the stimulants such as coffee and 


tea; and, among the careless, of the depressants of the alcohol 
group. The stimulants owe their action to the presence of 
of the alkaloid, caffeine, a drug that excites the cerebrum 
through increasing the blood supply and through some 
obscure effect on the cerebral cells. The depressants owe 
their activity to the narcotizing effect of alcohol on the nerve 
cells, resulting in a progressive inhibition of the higher 
faculties ; this benumbing effect shows first on those faculties 
most recently acquired by the race in its upward develop- 
ment, and then proceeds downward in inverse order to that 

The main sequences in metabolism are summarized in 
Fig. 16 on page 66. 


Owing to the fact that the ''muscle is a protein machine 
for the accomplishment of work," any considerable activity 
of the muscles results in some protein katabolism, as indi- 
cated by an increase in the elimination of nitrogen by the 
kidneys, though experiments show that this increase of 
katabolic nitrogen is much less than might be anticipated. 
But the changes in carbon dioxide excretion vary directly 
with the extent of muscle activity, as might be expected 
from the relation of muscle action to the dynamic factors 
involved. Even the vital processes are more active, and 
hence require more oxygen when one is in the sitting posture 
than when he is reclining; and this activity increases when 
one changes from the sitting to the standing position. Also 
in the period of quiescence accompanying sleep there is a 
marked diminution in the oxygen-carbon dioxide metabolism, 
and a limited diminution in the endogenous nitrogen elimina- 
tion; this, of course, is largely explainable by the lessened 
muscle activity. 

Some interesting effects on metabolism are produced by 
variations in the external temperature. When the outside 
temperature is sufficiently low to produce muscular tension 
as a reflex from the skin, there is a definite increase in the 


amount of carbon dioxide eliminated, but no perceptible 
increase in the nitrogen elimination. 


Lusk: The Science of Nutrition. 

Chittenden: Physiological Economy in Nutrition. 

Chittenden: The Nutrition of Man. 

MacLeod: Changes in Food Supply and their Relation to Nutrition. 

Mendel, Utihzation of Dextrose, Jour. Lab. and Clin. Med., 1917, 2, 112. 

MacLeod and Fulk: Retention of Dextrose in Liver and Muscles, Am. 
Jour. Phys., 1917, 42, 143. 

McDaniell and Underhill: Relation of Diet to Glycogen Content of 
Liver, Jour. Biol. Chem., 1917, 29, 255. 

MacLeod and Pearce: Adrenals and Sugar Production by Liver, Am. Jour. 
Phys., 1912, 29, 419. 

Wilder and Sansum: Sugar Tolerance, Arch. Int. Med., 1917, 19, 311. 

Cannon et al. : Emotional Hyperglycemia, Am. Jour. Phys., 1911, 29, 280. 

Bloor: Metabolism of Fats, Jour. Biol. Chem., 1916, 24, 447. 

Folin;. Metabolism of Proteins, Am. Jour. Phys., 1905, 13, 117. 

Kocher : Sparing Action of Carbohydrates on Protein, Jour. Biol. Chem., 
1916,25, 571. 

Shaffer: Creatinin Metabolism in Health and Disease, Am. Jour. Phys., 
1908, 23, 1. 

McCollum et al.: Fat-soluble A and Water-soluble B, Jour. Biol. Chem., 
1916,27, 33. 



Just as each individual cell must have its waste material 
promptly removed in order to avoid being poisoned by that 
waste; so the great aggregate of cells, the body, has to have 
promptly removed from its nourishing medium, the blood, 
the accumulating waste of tissue metabolism, as well as the 
excess of unutilized material that may accumulate in the 
blood stream. Not all of this waste material passes out 
through the same channel; the excess water passes out 
through the kidneys, lungs, skin, bowel, and secretory glands; 
the carbon dioxide is chiefly eliminated through the lungs, 
though small amounts find exit through the kidneys and 
skin; the nitrogenous waste, representing the end-products of 
protein metabolism, is eliminated almost exclusively by the 
kidneys, though minute amounts may escape through the 
bowels and skin. The significance of the various products 
found in the urine is of much importance in apprising the 
investigator concerning the several katabolic processes going 
on in the body, especially with the processes involved in 
protein katabolism; therefore it becomes necessary to study 
the composition of the urine, and the physiological meaning 
of the several components. 


L'^rine, the excretory product of the kidne^^s (Fig. 17), is 
a thin limpid liquid, having a normal average specific 
gravity of L020, varying in color from pale yellow to reddish- 
brown, possessing a reaction that may be acid or neutral or 
alkaline, having a peculiar aromatic odor and a very complex 
composition. The color is due to various pigments, hemic, 
biliary, and tissue— chiefly biliary. The reaction depends 



somewhat on the nature of the diet being acid when meat 
foods are eaten in abundance, and alkahne when vegetable 
foods predominate in the diet; the acid reaction is much the 
more common, and is immediately due to the presence in the 
urine of sundry acid salts, both organic and inorganic; the 
degree of acidity is greatest soon after meals, and declines 

Fig. 17. — Vertical section of kidney. (Gray.) 

to a low point as the interval between meals is prolonged. 
The substances responsible for the peculiar odor have not 
been isolated; probably they come in part from the food, as 
strongly indicated when asparagus has been eaten, and in 
part from the intestines. 

Constituents of the Urine.— The average total amount of 
urine passed in twenty-four hours is about 1500 cc; with the 



ordinary mixed diet, 40 gm. of this total will be composed 
of organic solids, and 25 gm. of inorganic solids. 

Organic constituents 

Inorganic constituents. 


35.0 gm 

Sodium chloride 

15.0 gm. 

Uric acid 

0.7 gm 


3.5 gm. 


1.0 gm 

Phosphates . 

2.5 gm. 

Hippuric acid 

0.7 gm 

Potassium salts 

2.3 gm. 

Other substances 

2.6 gm 

Ammonium salts 

0.7 gm. 

Magnesium salts 

0.5 gm. 

Calcium salts 

0.3 gm. 

Other substances 

0.2 gm. 

When the average normal amount of urine passed daily 
has been determined for any individual the proportionate 
amount of constituents that are normal may be computed 
from the above table. However, it must be borne in mind 
that the amount of the several constituents may be varied 
by many conditions, environmental and intracorporeal. 
The relative amount of water present in urine varies with 
the outside temperature and with the humidity, decreasing 
as the temperature rises and the humidity falls and increasing 
as the temperature falls and the humidity rises; this is, of 
course, largely a compensatory result of the relative activity 
of the sweat glands, as marked increase in the rate of perspir- 
ing is accompanied by a relative decrease in the amount of 
water excreted by the kidneys, and vice versa; consequently 
the amount of water in the urine will vary somewhat with 
seasonal changes, with the amount of water ingested in a 
day, with the degree of mental or bodily exercise, and by 
sundry emotional conditions. The amounts of solids in the 
urine will be affected somewhat by the quantity and nature 
of foods taken, by the physical and mental activities, and 
somewhat by atmospheric conditions. 

The principal determination made use of in urine analysis 
to find the relative protein katabolism is that of finding out 
the total amount of nitrogen present. It will be recalled 
that nitrogen makes up 16 per cent of the protein molecule; 
and since urea, creatinin, and the purin bodies all represerjt 
end-products of protein katabolism, a determination of the 
nitrogen present in the urine gives a basis for the estimation 


of the entire product. It has been ascertained, by many 
careful determinations, that in the average urine, of the total 
nitrogen present about 87.5 per cent is combined in the urea, 
about 4.3 per cent is combined in compounds of ammonia, 
about 3.6 per cent in creatinin bodies, about 2.5 per cent in 
purin bodies, and the remaining 2 per cent in substances of 
uncertain composition. 

Urea.— The urea in the urine is the chief form in which is 
eliminated from the body the end-products of protein and 
albuminoid katabolism. It is usually present in the ratio 
of about 20 gm. of urea to 1000 cc. of urine. Urea is derived 
from several sources; its principal source seems to be from 
sundry ammonia compounds formed by the cleavage of the 
proteins in the small intestine, by bacterial action in the large 
intestines, and by a urease to a slight extent in the tissues. 
These ammonia compounds, in the form of either a carbonate 
or carbamate are converted into urea by the liver. Another 
source of urea is from some of the mon-amino acid salts which 
coming to the liver are there deamidized, the ammonia 
group being converted into urea while the organic acid 
radicle is utilized in other synthetic processes in the body. 
Urea may also be derived from some of the diamino sub- 
stances, arginin for example. Thus, though urea is elimi- 
nated by the kidneys, it is formed as such in the liver, and 
represents largely the unutilizable ammonia group in the 
proteins of the food. As a consequence, the greater the daily 
intake of protein food the higher will rise the proportion of 
urea in the urine, if there arise no other compensating factors. 

Purin Bodies.— The purin bodies (uric acid, xanthin, 
hypoxanthin) are mainly derived as katabolic products 
from the nucleins of food (exogenous), and from the tissue 
nucleins (endogenous). From muscle protein, exogenous 
and endogenous, arise adenin and guanin by a process of 
cleavage; these are then deamidized, forming xanthin and 
hypoxanthin respectively; oxidation of these two latter 
products results in uric acid; and the uric acid immediately 
unites, of course, with alkaline bases in the blood to form 
urate salts. The amount of endogenous uric acid daily 
formed and excreted is fairly constant for each individual, 


amounting to from 0.15 to 0.20 gm. a day; this probably 
represents the daily detrition of nuclear material within the 

Creatinin.—Th.e daily elimination of creatinin is from 0.007 
to 0.011 gm. for each kilogram of body weight. Creatinin is 
apparently derived from the protein tissues of the body, and 
may be said to represent the waste resulting from the normal 
metabolism constantly going on in living tissue. 

Creatin.— Another product occasionally found in urine is 
creatin. It is sometimes found in the urine of rapidly grow- 
ing children; it is always found in the urine of puerperal 
women during the period of uterine involution; not infre- 
quently it is found in the urine in certain abnormal conditions 
like fevers and starvation. These facts seem to indicate 
that the presence of creatin in the urine betokens a condition 
of unusual destruction of body protein. 

Hippuric Acid.— The hippuric acid salts in the urine 
(about 0.7 gm. daily) are derived for the most part from the 
benzoic acid constituents of the vegetable portion of the 
diet; they also may be derived in small part from the bac- 
terial decomposition of proteins in the large intestine; much 
smaller amounts apparently are derived from some undeter- 
mined metabolic activities elsewhere in the body. The 
synthesis into hippuric acid is said to take place in the 

Inorganic Sulphates.— The inorganic sulphates appearing 
in the urine are derived largely from the sulphur molecule 
in the protein food; though a small part comes from the 
mineral sulphates in the diet where they exist as sulphates 
of the alkaline metals. 

Ethereal Sulphates.— The ethereal sulphates, occasionally 
present, are held to indicate approximately the extent of 
putrefaction going on in the intestine. Some of the products 
of decomposition in the large intestine (indol, skatol, phenol, 
and cresol) may be absorbed into the blood; if so, they will 
become oxidized and then united with the sulphur group to 
form the so-called ''conjugated sulphates;'' when so united 
they form innocuous compounds, hence this conjugation 
represents a method whereby nature protects itself against 


self-poisoning. Some of the colonic aromatics may unite 
with glycuronic acid forming their respective salts which 
are also relatively innocuous substances. 

Sodium Chloride. — The sodium chloride eliminated, 
amounting to about 15 gm. a day, is derived largely from the 
salt in the food, though a small part may come from the 
katabolized protein tissues of the body; this general state- 
ment holds true also of the other inorganic constituents of 
the urine. 

The Secretion of Urine (Figs. 16, 17 and 19).— How is the 
kidney able to select out of the blood those several waste 
products that are found in the urine? About this question, 
as around that one pertaining to exchanges taking place in 
the capillaries, has revolved a long controversy. The original 
theory of Ludwig proposed that the secretion of urine 
occurred in obedience to the simple laws of filtration, osmosis, 
and diffusion. A later school, the Bowden-Heidenhain, 
contended that these physical factors were inadequate; 
that there must be assumed a special secretory faculty on the 
part of some of the cellular elements by means of which 
faculty certain ingredients in the blood were selected by the 
cells, incorporated into their protoplasms, and then excreted 
distally into the collecting tubules. Other students believe 
that the physical laws are adequate to account for some of the 
phenomena but not all of them. In the face of such conflict- 
ing opinion it seems best simply to present what appears 
to be the more widely-accepted view. 

Glomerulus.— In the glomerulus, or Bowman's capsule 
(Fig. 19), takes place the elimination of the water, the gases, 
and the inorganic salts (and perhaps other crystal lizable 
material) ; with these the rate of elimination seems to depend 
considerably on the relative blood-pressure in the kidney. 
The physical laws of filtration, diffusion, and osmosis, seem 
adequate for the elimination of these substances, provided 
we accept the condition that the relative permeability of the 
glomerular epithelium may readily vary to meet changing 

Convoluted Tubules.— In the convoluted tubules (see Fig. 
18) takes place the elimination of nitrogenous material and 



other organic substances, and the resorption of some of the 
water and salt. This process of eHmination of nitrogenous 
material through the convoluted tubules seems strongly 
indicative of a specialized selective action on the part of the 

BowTmn's capsule Neck ist convoluted tubule 

Afferent vessel 
Efferent vessel 

Intertuhular capillaries 
Interlobular vein 

Interlobular artery 
Spiral tubule 

Henle'sf Ascending li-nd) 
loop \Descending limb 

Arterial arch 
Venous arch 

\ Cortical substance 

'':~:J^[-i\Pi: \ Boundary zone 


Duct of Bellini 

Fig. 18. — Scheme of renal tubule and its vascular supply, (Gray.) 

cells involved. As throughout the body various cells pick 
out those particular proteins needed for their metabolism, so 
similarly here the cells of the convoluted tubules seem to 
have the specialized function of selecting particular sub- 



stances from the blood stream, taking these substances into 
their protoplasm, and then excreting them in the same form 
or as a related form into the adjoining lumen of the tubule. 
This special activity of the tubule cells shows many imper- 
fectly understood oscillations in efficiency; but a prognostic 
explanation of these variations is not available. 

The diagram of Fig. 19 summarizes the main points in 
this theory of urine elimination. 

Arterial blood 

Venous blood 

V H20 

\ NaCI 

1 Bowman's 
/-<— capsule 






H2O & 






Fig. 19. — Diagram illustrating kidney activity in excreting urine. 

The urine passes through the collecting tubules on into 
the pelvis of the kidney and so into the ureters. The ureters 
force the urine onward by a series of rhythmic contractions 
which run in peristaltic waves from the kidney to the bladder. 
The urine is thus forced into the bladder in a series of spurts. 
Return of the urine into the ureters is effectively prevented 
normally by the oblique position of the ureters in passing 
through the bladder wall whereby the lumen of the ureter is 
kept compressed by the tonic musculature of the bladder 
except when urine is being forced through from the ureter. 

Because the muscle walls of the bladder are in a constant 
state of tonicity the present capacity of the bladder is equiva- 
lent to the present quantity of contained liquid. The tonic- 
ity seems to augment directly with increase of urine volume; 
this increasing tonicity of the muscle coat tends to bring 
about a reflex inhibition of the sphincter around the bladder 
exit (the sphincter vesicoe) with escape of the urine into the 
urethra. Normally this sphincter is under good volitional 
control so that urination takes place only as willed, though 
such control is not gained until late infancy, and in some 
nervous children, not until late childhood. With relaxa- 


tion of the sphincter vesicce, voluntary or otherwise, the urine 
is forced into the urethra by the compression of the bladder 
muscles, and normally flows unhindered through the urethra 
to the exit. At the termination of the flow the urethra is 
emptied of the few final drops by two or more peristaltic con- 
tractions of the muscles surrounding the urethra (the com- 
pressor urethroB and hulho-cavernosus) . 


Folin: Composition of Normal Urine, Am. Jour, Phys,, 1905, 13, 45, 
Van Slyke and Cullen: Urea in Urine, Jour, Biol. Chem., 1914, 19, 211. 
Hanzlik and Hawk: Uric Acid Excretion, Jour. Biol. Chem,, 1908, 5, 355. 
Bush: Competency of the Uretero-vesical Valves, Am, Jour. Phys., 
1924, 68, 1, 107. 

Bush: Kidney and Trigone, Jour. Lab, and Clin. Med., 1924, 9, 11. 



The heart (Fig. 20) is a great pump whose function is to 
keep the stream of blood continuously flowing through the 

Uight coronary 

Ant, desc. branch of left 
coronary artery 

Fig. 20. — Sternocostal surface of heart. 

vessels of the entire body. Its action is intermittent, but 
the bloodflow is maintained at a fairly constant rate through 
the elasticity of the arteries. The real work of the heart is 



divided into two parts; the lesser part, that of forcing the 
blood through the lungs, being performed by the right ven- 
tricle; while the greater task, that of forcing the blood over 
the balance of the body, is effected by the left ventricle. 
The action of the two sides is practically synchronous. 

To the head and upper extremities 
To the lur „ 

From the head, chest 
and upper extremities 

From all the body below 
the diaphragm 

To all the body below 
the diaphragm 

Fig. 21. 

-Diagram illustrating the course (A, B, C, D, E, F,) of blood 
flowing through the heart. 


The blood enters the right auricle of the heart from the 
two great veins {venoe cavce) that bring the blood in from the 
entire body; from the right auricle the blood passes through 


the right auriculo-ventricular opening into the right ventricle, 
thence to the lungs by way of the pulmonary artery, from the 
lungs through the pulmonary veins to the left auricle, then 
through the left auriculo-ventricular opening into the left 
ventricle, then out into the aorta to be distributed all over 
the body. The filling of the chambers of the heart (the 
auricles and ventricles) is termed the period of diastole; the 
emptying of those chambers is termed the period of systole. 
Auricular diastole precedes ventricular diastole, and auricular 
systole precedes ventricular systole. 

Action of the Auricles.— In diastole the auricles are passive 
and relaxed, and the blood flows into them from the great 
veins until distention reaches the point of muscular resistance; 
then an extremely rapid contraction wave, starting at the 
point which lies between the entrance of the great veins, 
empties the blood from the auricles into the ventricles. Fol- 
lowing the path of less resistance the blood passes through 
the auriculo-ventricular openings instead of back into the 
great veins; but since the orifices of these veins is not guarded 
by valves, the normal onward flow of blood from the veins 
is momentarily checked and rather forcefully; the auricular 
contraction producing this momentary cessation of flow 
induces a reverse pulsation wave that travels an indefinite 
distance back along the supplying veins. 

Action of the Ventricles.— During the latter part of the 
auricular diastole some blood is flowing into the passive 
ventricles. This filling of the ventricles is completed by the 
auricular systole; the contraction of the auricle is followed 
almost instantaneously by the contraction of the ventricles; 
this ventricular systole very energetically forces the blood 
from the right ventricle through the pulmonary artery to 
the lungs, and from the left ventricle into the aorta and thence 
to all parts of the body. Return of the blood during systole 
from the ventricles into the auricles is effectively prevented 
by the prompt pressure closure of the auriculo-ventricular 
valves. Likewise the ventricles are protected from any 
backflow from the great arteries by the strong semilunar 
valves placed at the arterial inlets. These valves are forced 
open very soon after the beginning of ventricular systole 


because the pressure within the ventricles becomes greater 
than that in the great arteries ; at the termination of ventricu- 
lar systole this intraventricular pressure rapidly falls to a 
point less than that in the arteries, with the result that the 
back pressure against the concave side of the guarding valves 
forces them into the closed position. 

Time Relations of the Cardiac Cycle.— With a pulse-rate 
of seventy times to the minute, the approximate time rela- 
tions of the different phases of the completed heart action 
are as follows: 

Auricular diastole, and pause 0.72 second 

Auricular systole 0.15 second 

Ventricular diastole, and pause 0.48 second 

Ventricular systole . . . . 38 second 

The time relations of auricular systole overlap somewhat 
those of ventricular diastole; and the time relations of auric- 
ular diastole overlap somewhat those of ventricular diastole. 
The relation of one to the other may be better comprehended 
by careful study of the diagram in Fig. 22; in the upper part 
of the diagram is represented a curve taken from the carotid 
artery showing the variations in pressure in the artery pro- 
duced by the various parts of the cardiac cycle; in the middle 
portion is a time scale graduated in tenths of a second, and 
three correlations of cardiac condition during any fraction of 
a second; in the lower portion is represented a series of six 
pumps showing positions of pistons and valves carefully 
correlated to the variations shown in portion 1 and 2. 

Any increase in the rate of the heart-beat is usually at the 
expense of the pause following diastole; later, as the rate 
increases excessively, the time will be taken also from the 
period of diastole. 

Action of the Heart Valves. — The auriculo- ventricular 
valves open very promptly after the completion of ventricu- 
lar systole. As the ventricles receive their impulse of blood 
from the contracting auricles, reflex blood currents press up 
against the rear of the auricular valves tending to close them; 
these valves are then forced into a tightly closed position at 
the beginning of ventricular systole by the greatly increased 
intraventricular pressure; but the valve leaflets are normally 



kept from being inverted back into the auricle by the leash 
action exerted by the musculi pectinati. With further increase 
of the intraventricular pressure the semilunar valves, lying 
between the ventricles and the aortae, are forced open and 
the blood in the two ventricles is forced out into the respective 

1 , 1 < 1 , 1 < 1 , 1 1 1 I 1 1 1 < 1 , 1 < 1 1 i 

0. I sec. 

1 A. Systole j| Auricular Diastole 

II A.Systoie 1 

Ventricular Systole | Ventrici 

jjar Diastole | 

1 1st Sound 1 2nd|Sound | 



x-l: \^ 

a=auricle; 6=.ventricle; c^venous inlet; (^=arterial outlet; e= mitral valve; J= aortic valve* 
Fig. 22. — Curve and time relations of a single heart-beat. 

systems. At the termination of ventricular systole the pres- 
sure within the ventricles falls to a point below that of the 
pressure in the pulmonary artery and the aorta, and the 
back pressure in these two arteries causes the semilunar 
valves to close sharply. 



On listening at the chest over the cardiac region there 
may be heard at each beat of the heart two sounds following 
each other in quick succession; each sound is followed by a 
brief interval of silence, the interval being longer after the 
second sound than after the first. These sounds may be 
imitated approximately by pronouncing the syllables loo oop. 
The sharpness of each sound, but especially that of the second 
sound, will vary considerably with variations in the relative 
tension within the arteries; the greater the tension, the 
sharper the sound. The relative length of time of the two 
sounds is 0.14 second for the first sound, with an interval 
of 0.2 second, and 0.08 of a second for the second sound with 
a succeeding interval of 0.4 second. The first sound is heard 
just at the beginning of systole while the second sound is 
heard just at the termination of systole. The first sound 
takes place at the inception of ventricular contraction and 
is chiefly due to the thud of the sharply-closed auriculo- 
ventricukr valves; but the sound is accentuated by the 
forward-thrusting impact of the heart against the chest 
wall, and by the quiver of the contracting ventricular mus- 
culature. The second sound begins just as contraction of 
the ventricles ends, and is due to the sharp closure of the 
semilunar valves. Sometimes a third sound is heard very 
soon after the second sound; it is very soft, and is ascribed 
to the vibration of the auriculo-ventricular valves caused by 
the inrush of blood from the auricles. 

The first sound is heard most favorably near the apex 
beat, that is in the interspace between the fifth and sixth 
ribs, 1 inch below and IJ inches to the right of the left nipple; 
the second sound is heard most readily in some subjects in 
the second right interspace just adjacent to the sternum, 
but in many subjects it sounds most clearly in the region of 
the apex beat. These positions are not immediately in front 
of the valves in question (Fig. 23), but the sound as heard 
is a transmitted sound, and the direction of transmission is 
such as to make the positions indicated the most favorable 
for listening. When a valve is diseased so that it gives rise 



to some adventitious sound, that sound is carried along: 
somewhat with the blood stream; so the physician will 
listen for abnormal sounds at points a little beyond the origin 
of the sound in the direction of the stream flow. 

Carotid tubercle 

Apex of lun 
Brachial plexus 
Subclavian arterj 
Acromial end of clavicl 
Lesser tuberosity 
Teudou of biceps 
Greater tulierosi' 
of hamerub 

'" ■ b 

Exterijal jupular vein 
f'ncoid cartilage 

thmus of thyroid gland 
Sternal head of stemo-inastoid 
( la\ icular head of sterno-mastoid 

Stemo claMeular articulation 
I- ir--t part axillary artery 
racoid process 

Fig. 23.— Anterior aspect of neck and shoulders, showing position of heart 
(After Cunningham.) 


The rate of the heart-beat varies at different periods of 
life, and is altered as to rate and rhythm by many conditions. 
The following table gives the variations due to age: 

Before birth . 
At birth . . . 
During first year . 
During second year 
During third year 

140 to 150 
140 to 130 
130 to 115 
115 to 100 
100 to 90 

At seventh year 
At fourteenth year 
Adults . . . . 
Old age 
Debility . . . 

90 to 85 
85 to 80 
80 to 70 
70 to 60 
75 to 65 

This table represents an average; the normal for some indi- 
viduals may be 10 or 15 beats above this average, and for 
others as much below the average. 

The rate with women averages 8 to 10 beats a minute 
higher than with men; the rate with small or short people 
is usually higher than with large or tall people. The rate 
varies with posture; it is at its individual lowest when the 
subject is lying down, about 10 per cent higher when the 


subject is in the sitting posture, and rising an additional 10 
per cent when the subject comes to a standing posture. 
Bodily activity causes a marked increase of the heart-rate; 
the continuance of acceleration depending on the length and 
severity of the exercise. Moderate activity, like the climb- 
ing of three flights of stairs, gives a normal average accelera- 
tion of from 25 to 30 beats a second; but this rate of increase 
diminishes in ten seconds to a plus of 15 beats to a second, 
and with those in prime health and condition the rate of 
beat will return to the normal within thirty seconds. How- 
ever, if the exercise be more severe, like running a considerable 
distance, the pulse-rate may continue in an accelerated con- 
dition for a half hour or longer; the persistence of accelera- 
tion depends largely on the degree of accumulated deficiency 
of energy-yielding material and on the accumulated excess 
of katabolites. 

If the carbon dioxide content of the blood is increased, 
or if the oxygen content is markedly decreased, there ensues a 
centric stimulation of the heart in a reflex attempt at com- 
pensation; if the variation of either gas be altered 10 per 
cent, and if the heart-rate becomes adaptively changed so 
that the volume of gas moving by a given point becomes 
the same per unit time, then the adaptation of heart-rate to 
body needs is fully compensatory; but if compensatory relief 
be not afforded, an increasing toxicity soon weakens and 
diminishes heart action. 

In laboratory experimentation alterations in the chemical 
percentage constitution of the blood affects the rate of heart 
action; for example, increase in relative amount of either 
the potassium or the sodium content of the blood produces 
a decrease in the rate and efficiency of heart action, while an 
increase in the calcium content, within relatively narrow 
limits, causes an increase in both rate and amplitude of heart 
action. However, there is no proof available that any effec- 
tive alteration of these constituents of the blood ever occurs 
in the human body, at least in health. 

The rate of heart action usually shows a compensatory 
adaptation to variations in intravascular pressures. When 
the blood-pressure falls, there is usually a sufficient quicken- 


ing of the heart to enable it to force an adequate amount of 
blood to the vital centers in unit time; and when the blood- 
pressure is high, there is usually a compensatory slowing of 

Sensory and emotional disturbances profoundly alter the 
heart-rate, usually increasing both force and frequency; this 
is an adaptive response whereby the body is furnished 
increased amounts of energy-yielding material per unit time, 
with a more rapid elimination of katabolites, the better to 
enable it to meet impending dangers, or threats of such 
dangers, or to expend unusual amounts of energy. 

The rate usually increases both in force and frequency 
after meals, probably as a compensation for the active 
splanchnic dilatation. 


Many careful observations point to the conclusion that 
each ventricle expels from its cavity about 80 cc. of blood 
at each beat of the heart, under average normal resting 
conditions. The resistance offered by the arteries and their 
contents amounts to about the pressure equivalent of 0.15 
meters of mercury, in the aorta, and to about 0.06 meters 
of mercury, in the pulmonary artery. Therefore the work 
done by the heart at each beat is equal to the product of the 
load lifted when multiplied by the resistance, or height to 
which the load is lifted. And then this must be multiplied 
by the factor 13.6 which represents the density of mercury 
as compared with the density of blood. Then: 

80 times 0.15 times 13.6 equals 163.2 for the left ventricle. 
80 times 0.06 times 13.6 equals 64.28 for the right ventricle. 

These products represent grammeters of work, since the 
80 cc. weighs about 80 gm. ; this multiplied by the height to 
which the load is lifted gives a product in grammeters. These 
two added together amount to 227.48 grammeters of work. 
But to this amount must be added whatever force is required 


to give the blood stream whatever velocity it acquires. The 
velocity of the blood as it leaves the heart is estimated to be 
about 0.5 meter per second. Making use of the formula 

w = ^ (in which w equals work done, p equals weight moved, 

V equals velocity of movement, and g equals acceleration due 

to gravity), and substituting the numerical equivalents, the 

/ 80 X. 5^ 
results would be 1 .02 grammeters of work ( w = - — -^ = 1 .02 

\ z X y.o 

for each ventricle; adding this to the above gives a total 
amount of work performed by the heart at each beat equiva- 
lent to 229.52 grammeters. Assuming the average heart- 
rate throughout the day to be 70 beats a minute, then the 
total work performed by the heart in twenty-four hours 
would be equivalent to 23,000 kilogrammeters. 

It is well to note that the volume of blood expelled from 
the heart varies greatly according to the condition of bodily 
activity. It is claimed that this volume may be as low as 
40 cc. at a beat, when the subject is at rest, or as high as 
220 cc. at a beat when the subject is vigorously active. 


When the auricles are filling, and as the blood flows into 
the ventricles, the intracardiac pressure is equivalent to 
about one atmosphere, but it slowly rises to its auricular 
maximum at the moment of auricular contraction. The ten- 
sion within the ventricles increases steadily during the period 
of their systole; the first result of this increasing tension is 
the closure of the auriculo-ventricular valves; then the semi- 
lunar valves are forced open even against the high pressures 
existing in the aortse. At the termination of ventricular 
systole, the intraventricular pressure rapidly falls until first 
below that in the aortse, when the semilunar valves sharply 
close, then second below that in the auricles, whereupon the 
auriculo-ventricular valves open and permit the inflow from 
the auricles. 



During the period of diastole the heart is flattened and 
lax, somewhat elongated with the base elliptic in its vertical 
plane with the short diameter of the ellipse running antero- 
posteriorly. During the period of systole the heart becomes 
more conic in shape, nearly circular in its vertical plane, 

Posterior surface. Anterior surface. 

Fig. 24. — Showing changes taking place in the contour of the heart dur- 
ing contraction. (Dotted Hne = diastole; solid line = systole). (After 

slightly shortened in its long diameter, hard and firm (Figs. 
24 and 25) . The apex of the heart becomes somewhat rotated 
downward, and to the right, resulting in its hitting the chest 
wall with a distinct thud. The forward thrust of the heart 
is due to the stiffening and straightening of the arch of the 
aorta from the sharp thrust of the entering volume of blood; 
the movement of rotation is due to the spiral course of the 
muscular fibers running from the fixed base downward in a 
w^inding fashion from rear to front to the freely-movable 



apex, and thus producing on contraction a swing of the apex 
forward and to the rii^^ht. 

Fig. 25. — Change in contour of the base of the heart during contraction, 
(Dotted Hne = diastole; soHd Kne = systole just at the close of the period.) 
A = pulmonary valve between the right ventricle and the pulmonary artery; 
B = aortic valve between the left ventricle and the aorta; C = mitral valve 
between the left auricle and ventricle; D = tricuspid valve between the 
right auricle and ventricle. (After Spalteholtz.) 

Properties of Heart Muscle.— The striated muscle of the 
heart manifests some distinctive properties as follows : 

1. Contractions of the heart muscle at any given moment 
are maximal for that present condition, regardless of external 
stimuli. (This is a laboratory finding on the heart muscle 
of the frog; whether or no it is true of human heart muscle 
is undetermined although thought to be so.) 

2. During the period of contraction the heart muscle is 

3. The heart muscle is in a constant state of tonicity 
whereby the cavities of the heart are constantly calibrated 
to systemic demands. 


4. The heart muscle throughout normal life maintains a 
regular sequence of action ; its force and frequency may vary, 
but its rhythmicity is an inseparable property of cardiac 

5. The rhythmic action of the heart is automatic; that is, 
the effective stimulus to contraction is self-generated and is 
not produced by external factors. External factors may and 
do alter the force and frequency of heart action but they do 
not create this action; what the inner stimulus is that induces 
a contraction is unknown, though it has been found that 
certain salts of metals seem to exert an important influence. 

Calcium, Potassium, and Sodium Action on the Heart.— Cer- 
tain experiments show that an isolated mammalian heart 
may be kept beating for a long time if constantly irrigated 
with oxegenated Locke's solution (NaCl, 0.9 per cent; CaCl2, 
0.024 per cent; KCl, 0.042 per cent; NaHCOs, 0.02 per cent; 
dextrose, 0.1 per cent). No substitution of other salts results 
in as favorable action; and the absence of any one of the 
first three results in a much earlier cessation of the heart's 

While much uncertainty exists as to the chemical reactions 
going on within the heart, the following conclusions are 
tentatively accepted : 

{a) When the sodium salts are not present in the irrigating 
solution the irritability and contractility of the heart both 
disappear; when the sodium salt is the only one present, a 
great relaxation of the heart promptly appears. 

(5) When the calcium salts are absent from the irrigating 
solution the heart muscle becomes greatly relaxed; when 
these salts are the only ones present, or are present in excess, 
the tonicity of the heart muscle becomes greatly accen- 
tuated, sometimes to the point of resulting in a continuous 

(c) The potassium salts do not seem to be so essential, 
though they appear to augment the action of the sodium 
salt in producing relaxation; when they are present in excess 
they markedly slow the heart and may inhibit its action 

Thus it will be seen that these salts apparently exert a 


profound influence on the heart's action, but whether they 
originate the inner stimulus through electric or chemic 
reaction with the living tissue, or whether they are vitally 
accessory to that stimulus is problematical. It is known that 
these salts are present in human blood in about the same 
proportion as optimal for the irrigating solutions; it is not 
know^n whether they become increased or reduced in health 
or disease, but probably they do not vary very much from 
the relative percentages indicated. 

The Contraction Wave of the Heart. — ^The contraction wave of 
the heart starts at the sino-auricular node located in the sulcus 
terminalis between the entrance of the superior vena cava and 
the superior aspect of the auricular appendix, which area 
represents all that remains of the first chamber of the original 
pulsating tube. From the sino-auricular node the impulse 
of contraction spreads with great rapidity over the entire 
auricular muscle, then passes through the auriculo-ventricular 
fasciculus, or bundle of His, to the musculi papillares thence 
through the vortex of fibers surrounding the apex and thence 
back to the base of the heart. This sequence of the con- 
traction wave has not been demonstrated to complete satis- 
faction, though much of the accumulating data indicate its 
essential probability. 

Observations made on excised frog hearts— hearts com- 
pressed by atriatomes, hearts incised, hearts cut into long 
strips, and studies made on the connections of the bundle of 
His— have led to two hypotheses concerning the manner of 
the heart-beat; one school claims" that the automacity is 
controlled by intrinsic ganglia, the other school claims that 
this control is muscular. 

The first school, those who hold to the neurogenic theory, 
assume that the initial impulse arises in the sino-auricular 
region in motor ganglionic cells, and that the contraction 
impulse spreads over the heart muscle by means of a system 
of connecting coordinating intrinsic nerve cells and fibers. 
Unfortunately for this theory the histological evidence is 
far from confirmative. 

The second school, those who hold the myogenic theory, 
assume that heart muscle is inherently automatic; that within 


the muscle itself is initiated the cardiac activity; and that 
the demonstrable nerves and ganglia simply serve to regulate 
more or less completely the rate and force with which that 
rhythmicity is expressed. The evidence to substantiate this 
contention is adduced as follows : 

(a) The heart of the embryo chick pulsates before any 
nerve cells or fibers appear in it. 

(6) Isolated portions of the pulsating heart of the embryo 
chick may be kept alive in a suitable blood-plasma medium 
wherein it will undergo differentiating multiplication pro- 
ducing new muscle cells which in turn exhibit the phenomenon 
of rhythmic contractility. 

(c) Minute strips of heart tissue taken at random (from 
cold-blooded animals) exhibit rhythmicity; can each little 
piece have its own motor nerve center? 

{d) TAgzdig incisements of the heart, which would presum- 
ably sever all nerve continuity, do not prevent contraction 
waves from sweeping over the entire muscle. 

It will be noted, however, that this controversy between 
the neurogenists and the myogenists is concerned with the 
manner in which the inner impulse is propagated from the 
point of initial impulse to all other portions of the heart; it 
makes no attempt to solve the nature of that inner impulse; 
this latter problem is more occult. 

Nutrition of the Heart.— The heart itself receives its main 
supply of blood through the coronary arteries (see Fig. 26) 
with an additional important supply through the Thebesian 
orifices. The right and left coronary arteries have no inter- 
communication except indirectly though inosculating capil- 
laries. The arteries are injected once at the beginning of 
systole, but quickly undergo obliterative compression near 
the end of systole from the general squeeze of the encompass- 
ing muscle; when this pressure is released, just at the begin- 
ning of diastole, there is a second sharp injection of the coro- 
nary arteries from the back pressure in the aorta. Thus 
there is produced a very rapid flow of blood through the 
vessels of the heart, effectively providing for the relatively 
tremendous need of the heart for oxygen and nourishment. 



Bight vagus 
Eectirrent laryngeal 

Left vagus. 
Left phrenic. 
Thoracic duct. 

Fig, 26, — The arch of the aorta, and its branches. (Gray.) 


The Cardiac Nerves.— Though the action of the heart is 
automatic, its rhythm is sensitively subject to many factors 
some of which have been discussed already. The response 
of the heart to meet bodily needs and conditions, and to 
adaptively protect it from marked variations in peripheral 
resistance, is brought about through a system of extrinsic 
nerves which proceed to the heart from autonomic centers in 
the central nervous system. The nerves coming from the 
cranial area convey impulses that cause a decrease in both 
the force and frequency of heart action, and hence are 
termed inhibitors; those coming from the spinal area convey 
impulses that cause an increase in both the force and fre- 
quency of heart action, and hence are termed accelerators 
or augmentors. There are also sensory fibers running from 
the heart and aorta conveying impulses concerning the 
present condition of the heart and aorta; these impulses 
eventuate in motor reflexes of adjustment of heart-rate and 
force to meet vascular conditions elsewhere in the body. 

The inhibitory fibers, which are found in all vertebrates, 
come from the cerebral medulla by w^ay of the tenth, or 
vagus, nerves; these pass into the cardiac plexus as branches 
of the superior and inferior cardiac nerves. Through experi- 
mental work it has been ascertained that the action of the 
impulses coming along these fibers is to slow and weaken 
the action of the heart, especially the phase of diastole 
(Fig. 27) ; they seem also to produce a diminution in conduc- 
tivity of the bundle of His. Opinions difl^er as to whether 
auricle and ventricle are both affected; probably the major- 
ity of observers incline to the view that the action is exerted 
on the auricle only, and perhaps on just the sino-auricular 
node. Irritation of sensory surfaces, like that present in 
acute gastritis, often produces a reflex slowing action on the 
heart; this reflex assumedly is acting through the medul- 
lary area from which the vagus fibers to the heart arise— 
the cardio-inhibitory center— thus producing an increase of 
vagal impulses. This center is also acted upon by reflexes 
from the cranial nerves and by reflexes from the higher cranial 
centers, by intracranial pressures, and by alterations in the 
composition of the blood stream. 


The cardio-inhibitor center is in a state of constant activity, 
the degree of which varies with sundry systemic conditions. 




Time = 1 

Fig. 27. — Result on heart action of turtle of brief electric stimulation of 

right vagus. 

Probably every impulse sent out by the center is due to a 
series of afferent impulses coming from the heart, or from 


the bloodvessels, or sensory surfaces, or basal ganglia; thus 
the center serves as a balance regulator. If the afferent 
impulses are such as to irritate the center, there results a 
slowing of the heart-rate ; but if the center is depressed, or is 
relatively inactive, then the rate of the heart may be increased 
through uncompensated impulses coming to it from the 
accelerator center. Under normal conditions probably the 
center is activated more by afferent impulses from the heart 
and aorta, along the so-called depressor nerve, than by any 
other single factor; thereby the heart maintains its own 
balance, for the most part. 

The exact nature of inhibition has not been determined, 
but it is known not to be due to either the nature of the nerve 
fibers going to the heart or to the quality of impulses sent. 
Experiments by Howell tend to indicate that heart inhibition 
is due to an increase of the depressor action of the potassium 
salts; but whether there is here involved an increased sus- 
ceptibility to the potassium ion or an actual increase of the 
potassium ions through productive diffusion, is as yet a 
matter of speculation. 

The action of the inhibitory nerves is somewhat balanced 
by another set of ner\'es coming to the heart from the spinal 
cord. The action transmitted by these fibers serves to aug- 
ment both the force and frequency of the heart's activity, 
though the increase in rate is usually more noticeable than 
the increase in amplitude. Though no definite accelerator 
center has been discovered, one is assumed to exist some- 
where in the medulla; and like the inhibitor center, it is 
assumed to be in a state of constant though variable activity. 
Thus these two centers, the cardio-inliibitor and the cardio- 
accelerator, are normally antagonistic, and serve thereby to 
further serve a nicety of balance of heart action. Each 
center is affected by sensory and emotional stimuli; but the 
relative extent of such action on this center or that is difficult 
to exactly determine inasmuch as depression of one center 
has the same apparent effect as stimulation of the other 
center. That they have independent action, though, is well 
shown by the following experiments: If the peripheral ends 
of the cut vagi be moderately stimulated so as to maintain a 


slowed rhythm of the heart, an acceleration will be produced 
by some stimuli but not by others; if the accelerator fibers 
(in another experiment) be cut, muscular activity will not 
now produce an increase in heart action. Thus there seems 
to be a compensatory balancing activity between these two 
regulative centers whereby adjustments of heart-rate to sys- 
temic need are more or less effectively controlled. 



Like other muscles the heart muscle manifests a contrac- 
tion change of electric potential. This electric potential 
falls first in the neighborhood of the auricles, next in the 
region of the papillary muscles near the apex, then in the 
region of the base of the ventricles, and this is followed by a 
rapid fall in the vicinity of the apex. The fall of potential 
precedes the wave of excitation. 

A graphic registration of these variations in the electrical 
condition of the heart may be made by photographing the 
oscillations made in the string of a string galvanometer 
which is in connection with the subject. The Q wave is 
thought to represent the fall in potential just preceding 
ventricular contraction; the R wave may represent the 
change in potential accompanying the actual contraction, 
followed by a reverse condition as indicated by the S wave; 
the significance of the T wave has not been satisfactorily 


When the blood has been forced out of the heart it passes 
into the arterial system for distribution all over the body; 
it is then collected by the venous and lymphatic systems 
for its return to the heart and lungs. Because of the branch- 
ing and subbranching of the arteries, and because of varia- 
tions in the elasticity of the arterial walls, there is a continu- 
ally diminishing change in the velocity of the blood stream, 
and in its lateral pressure; both diminish rapidly to the capil- 
laries, and increase less rapidly in the veins. This alteration 
in velocity and pressure is due to the total relative size of the 
stream bed at any point selected toward the capillaries, since 
the cross areas of all the branches is greater than that of the 
parent stems. Vierodt has estimated that the combined 
cross area of all the capillaries is about eight hundred times 
the cross area of the aorta; hence, according to the laws of 
hydrodynamics, the lateral pressure and the velocity of flow 
will be about one eight-hundredths of that obtaining in the 

The velocity of the flow of the blood is affected by the 
energy of the heart's contraction, by the width of the contain- 
ing vessel, by the distance of the vessel from the heart, by 
the present elasticity of the vessel, and by the absolute 
amount of blood in the body. Experiments by Vierodt 
indicate that the normal velocity of blood in the capillaries is 
about 0.6 mm. per second; then, from his previous estimate 
as to the relative size of capillary and aorta, the aortic 
velocity ought to be about 480 mm. per second. Actual 
experiments performed with suitable apparatus on animals 
give the following results: Carotid of the horse, 520 mm. a 
second during systole but 150 mm. a second during diastole; 


in the dog, 260 mm. a second in the carotid artery, 147 mm., 
a second in the jugular vein, 61 mm. a second in the femoral 
vein, 63 mm. a second in the renal vein, and 85 mm. a second 
in the mesenteric vein. 

The time for complete circulation of the blood has been 
estimated as from fifteen to thirty seconds; but the time 
depends a great deal on the circuit selected and on the extent 
and location of the capillaries involved. 

There are several factors involved in the maintenance of 
the circulation of the blood. The leading factor is the con- 
traction of the ventricles whereby a given volume of blood is 
forced against a considerable resistance into the seemingly 
full aorta and bloodvessels. The next factor in importance 
is the elasticity of the arteries which first yield to accommo- 
date the sudden increase in volume then contract with con- 
tinuous pressure on the contained liquid. Lesser factors 
are the contractions of the skeletal muscles, which compress 
capillaries and veins and so force onward the hemic contents; 
thoracic aspiration, which facilitates and expedites the move- 
ment of the blood in the great veins; and the venous valves, 
which prevent any marked damming back of blood through 
the force of gravity. 


When one considers that at every heart-beat about 80 cc. 
of blood is pumped into a vascular area already full; that the 
highly-elastic bloodvessels are markedly distended to accom- 
modate the increased volume, but rapidly compress about it; 
furthermore, that the resistance in the capillaries to the 
prompt passage of this volume is considerable; it is not diffi- 
cult for him to realize that there must be a marked intra- 
vascular pressure. This pressure is measured in man by 
finding out how much air pressure, as measured by the weight 
of a column of mercury displaced, is required to obliterate by 
external pressure the lumen of the more superficial arteries, 
it having been previously determined in experiments on 
animals that this occluding pressure is practically equal to 
intravascular pressure at that point. Complete obliteration 


of the lumen of the vessel measures the resistance, then, 
against maximal intravascular pressure; this, in the case of 
the arteries, represents systolic pressure. If now the external 
pressure be partially diminished so that the bloodvessel 
becomes widely distended during systole but flatly collapsed 
during diastole the amount of external pressure being used 
will represent intravascular pressure during the cardiac 
phase of diastole. The difference between systolic pressure 
and diastolic pressure is known as the pulse pressure. 

The average systolic pressure in young adults, as recorded 
at the brachial artery, is about 115 mm. of mercury; the 
average diastolic pressure at the same age is about 75 mm. Hg. 

The pressure in the pulmonary artery has been found to 
be, in animals, about one-eighth of that in the carotid 
artery; if the same ratio holds true in man, then this pressure 
maybe estimated to be about 20 mm. Hg., as the carotid 
pressure in man is about 160 mm. Hg. The velocity of this 
lesser circulation is considerably higher, however, than that of 
the greater circulation. 

Variations in Blood-pressure.— Under normal conditions the 
average blood-pressure steadily increases with age; it is 
about 110 at the age of fifteen, 115 at twenty; 120 at thirty, 
135 at forty-five and 145 to 170 at sixty years, an increase 
of about one point for each additional year after the age of 
thirty years. The pressure varies directly with the force 
and frequency of heart action, in health, and increases or 
decreases with like changes in peripheral resistance. In 
this connection, however, it must be recalled that heart 
action and peripheral resistance are usually balanced in 
action so that one increases as the other diminishes. There- 
fore any condition which tends to increase either of these 
forces without at the same time securing adequate compensat- 
ing influence on the other will result in a more or less tem- 
porary increase in blood-pressure. Thus, there is an increase 
of blood-pressure following meals, during and after exercise, 
accompanying mental activity, following change of posture 
toward the vertical, and as a result of the diurnal accumula- 
tion of stress. 

The pressure in the capillaries has been estimated as about 


35 mm. Hg. in the skin of the hand, and as abont 20 mm. Hg. 
in the ear; this, of course, represents the amount of external 
pressure required to obhterate the hnnen of the capillaries. 

Similar experiments on the veins show curious variations. 
In the brachial vein, when the arm hangs pendent, the 
obliteration pressure amounts to about 9 mm. Hg., but this 
pressure falls to zero if the arm be elevated. In the veins 
of the lower extremities the pressure is just enough to move 
the column of blood beyond the distal valve, which valves 
protect the thin-walled vein from the gravitation pressure 
of the superincumbent column of blood. In the veins near the 
heart the pressure is negative due in part to the aspiratory 
effect of reduced intrathoracic pressure during inspiration. 

This intrathoracic pressure in the mediastinum is less than 
one atmosphere since from the normal intrapulmonic pres- 
sure, which of course is atmospheric, must be deducted the 
pressure exerted by the elastic recoil of the lungs. The extent 
of this relative pressure may be determined experimentally 
by connecting a manometer with a trocar whose point has 
l^een thrust either into the mediastinal space or in between 
the pleurae. (Sometimes this is a necessary surgical procedure 
in severe inflammation of the pleura.) An actual experiment 
of this kind on man gave a negative pressure at the end of a 
normal quiet inspiration of — 4.64 mm. Hg., and at the end 
of a quiet expiration a negative pressure of — 3.02 mm. Hg. 
Forcible attempts at expiration as in straining with the 
glottis closed will abolish this negative pressure, and inci- 
dentally seriously check the upper circulation; conversely, 
forcible and deep inspiration will produce a marked increase 
in the negative pressure. This increase in negative pressure 
on inspiration, with an accompanying increase of positive 
pressure in the abdomen, facilitates the flow of blood through 
the thoracic vessels, thereby aiding the progress of the blood 

In man there is a slight fall of blood-pressure during inspi- 
ration resulting, assumedly, from the great veins dilating 
from reduced external pressure, and possibly from a slight 
accompanying diminution in the force of the heart's action. 



When the heart thrusts its ventricular content into the 
arterial system the highly elastic walls of the arteries dilate 
to accommodate their caliber to this sharp augmentation of 
volume. The first dilation takes place in the aorta^ of course; 
but as the stress wave rapidly progresses, each part of the 
arterial system quickly dilates in its turn ; this phase of dilating 
is immediately followed by a less prompt rebound of the 
elastic wall as it recoils on the flank of the wave and so forces 
a continuance onward of the flow of blood. This sequence of 
phenomena— acute dilation of an artery followed by its 
elastic recoil— is designated the pulse. The rhythm of the 
pulse is, of course, identical with that of the heart. 

The Velocity of the Pulse Wave.— This is calculated by 
obtaining records of the passing of the wave at two points 
whose intermediate distance may be measured fairly accur- 
ately. Records of the passing of such waves are best obtained 
on a swiftly-moving kymographion on which at the same time 
is being traced the record of a tuning fork beating in hun- 
dredths of a second. Observations of this kind show that the 
pulse wave travels at a velocity of about 7 meters a second, 
in the average young adult; in elderly people where the vessels 
are less elastic, the velocity is considerably greater. Inas- 
much as the period of systole occupies but three-tenths second, 
the pulse wave moving at the rate of 7 meters a second must 
reach with its beginning the furthermost arteries before the 
end of the wave has been completed at the cardiac end of the 

The pulse wave may be felt at any point where the blood- 
vessel is sufficiently superficial, such as at the wrist, the 
edge of the jaw bone, at the temple, inside the lower lip or 
at the side of the neck. By the sense of touch it is possible 
to determine the frequency of the pulse wave, its relative 
sharpness, its regularity, the relative compressibility of the 
bloodvessel, and the relative fulness of the arterial system. 
When more detailed information is desired it is customary 
to obtain a graphic record of the pulse wave; such a record 
is called a sphygmogram (Fig. 28). These sphygmograms 


show marked variations both as to different individuals, and 
as to the same individual under sundry conditions. The 
records of a given individual will vary from day to day and 
during the day, and will vary in relation to posture, meals, 
and exercise, both mental and physical. Variations appear 
in relation to age, sex, the condition of the heart and arteries, 
atmospheric and barometric conditions, emotional stresses, 
temperament, and other obscure influences. 

Fig. 28. — A time record of the pulse. (Howell.) 

Interpretation of the Sphygmogram.— The ascending limb, 
called the anacrotic, represents the incidence of the blood 
wave against the arterial wall, and records the approximate 
extent of yield to the pressure; the descending limb, called 
the catacrotic, represents the recoil of the elastic arterial wall. 
Normally the ascending wave shows no indentation but is 
perfectly smooth and straight; but the descending limb of the 
wave usually shows one or more secondary waves. The most 
pronounced of these secondary catacrotic waves, called the 
dicrotic notch, is usually assumed to be due to a secondary 
cardiac impulse produced by the abrupt closure of the semi- 
lunar valves; the other minor waves, distal to the dicrotic, 
are thought to be due to reflected waves from the various 
peripheral regions. 

By using a registering tuning fork in conjunction with 
the sphygmograph, it is possible to ascertain the duration of 
a pulse wave, and the time relations of its several parts. 
Accepting the finding that this duration is six-tenths second, 
on the average, and having previously learned that the 
velocity of the wave is 7 meters a second, it follows by com- 


putation that the length of the pulse wave is about 4.2 
meters, provided that the velocity of the wave is uniform. 
This is another indication that before the most proximal 
portion of the aorta has completely recoiled and resumed its 
normal caliber the initial impulse of the wave has reached 
the outermost arteriole. 

Venous Pulse.— Under normal conditions there is usually 
no venous pulse anywhere except in the great veins near the 
heart. If great vascular dilatation should occur at any point 
then the pulse wave might conceivably be carried through 
the capillaries and appear slightly in the continuing veins. 
Normally in the mn(E cavce, the subclavian and jugular veins, 
and probably also in the hepatic veins, there is a reflected 
pulse which may be variably perceivable. A sphygmogram 
of such a venous pulse shows a tracing in which one wave is 
thought to be due to the auricular contraction, and another 
wave thought to result from the ventricular systole. The 
quick descent of the base of the heart accompanying ven- 
tricular systole produces a sudden enlargement of the auricle, 
and this is represented by a long descending wave; filling of 
the auricle produces an ascending wave ; while opening of the 
auriculo-ventricular valve gives a second descending wave. 


Like the stomach, bowels, and heart, the bloodvessels 
have a regulative nerve mechanism that supplements their 
own intrinsic control and these nerves serve to secure a due 
balance of caliber of bloodvessels throughout the body. One 
set of nerves is called the 'vasoconstrictors because they serve 
to produce a diminution in the caliber of the bloodvessels 
to which they are supplied; if the supply is extensive, the 
result of such constriction will be a general rise of blood- 
pressure. The opposing set of nerves is called the vaso- 
dilators because, through producing a relaxation of the 
vascular musculature supplied, they induce an increased 
caliber of those bloodvessels; when the number of vessels 
so affected is large, the result of such vasodilatation is a 
general fall of blood-pressure. 


The vasoconstrictor fibers have their motor origin in 
an uncertainly defined area in the fioor of the fourth ven- 
tricle of the medulla near the origin of the fourth nerve. 
These fibers pass out of the spinal cord through the anterior 
roots of the nerves from the second dorsal to the second 
lumbar, thence going through the white rami to the sympa- 
thetic gangliated cord. Those destined for skin areas return 
from the gangliated cord as gray rami to be distributed along 
with the anterior and posterior divisions of the spinal nerves. 
Those destined for the viscera pass out of the ganglia of the 
gangliated cord, still as preganglionic fibers, and go thence 
by way of the splanchnic nerves to the celiac ganglion; out 
of this ganglion they go as postganglionic fibers to their 
destinations in the muscle coats of the bloodvessels. 

Sensory area 



Fig. 29. — Diagram illustrating vasomotor reflexes. 

These nerve fibers are transmitting tonic impulses constantly 
to the bloodvessels ; the number and quality of these impulses 
may be augmented or diminished by both centric and refiex 
influences. The center seems to be selective in its response 
to the needs of any region requiring vasoconstrictor action, 
but its activity is primarily determined by reflexes from 
sensory areas (Fig. 29); such reflexes apparently express a 
given area's need and may eventuate in either a stimulation or 
partial inhibition of the center's activity. Those fibers that 
convey to the center exciting impulses resulting in vaso- 


constriction are termed presstyr fibers ; their princip>al sensory 
distribution is to the skin. Those tillers that convey to the 
center inhibitory impulses resulting in diminished tonicity- 
of the center, and hence relative relaxation of the blood- 
vessels, are termed depressor fibers; they are found in fibers 
coming from the skin and other sensory areas, in many nerve 
trunks, and especially in fibers coming from the heart and 
arch of the aorta. 

The vasodilator fibers are believed to be entirely spinal in 
origin, no common center as yet having been discovered. 
The existence of such fibers has been satisfactorily demon- 
strated in the following nerves and areas : 

(a) In the chorda tympani branch of the facial nerve, 
distributed to the submaillary and sublingual glands, and 
to the anterior two-thirds of the tongue. 

(b) In the glosso-phar\TLgeal nerve, distributed to the 
parotid gland, to the posterior third of the tongue, and to 
the tonsils and phar\Tix. 

(c) In the cervical portion of the s\Tnpathetic, distributed 
to the ctitaneous region of the cheeks and neck, and to the 
mucosa of lips, gimis, nostrds and palate. 

(d) In the thoracic portion of the s^Tnpathetic, distributed 
through the splanchnic nerves to the abdominal \-iscera, and 
through the brachial and lumbar plexuses to the extremities. 

(e) In the first to third sacral nerves, distributed through 
the nerri erigentes to the erectile tissues of the genitals. 

These fibers do not transmit impidses that produce a 
condition of tonic acti\'it^'; the impulses transmitted are 
those which will adequately overcome the tonic influence 
of the vasoconstrictor impulses whenever circumstances 
demand engorgement of a vascular area. These impulses 
may be mental or emotional in origia, as well as sensory; but 
in the great majority of cases the impulses will be generated 
as reflexes from sensory areas, especially as r^ards glandular 
and visceral tissues. 

Either vasoconstriction or vasodilation promptly influences 
the volume of blood in the area affected. This change of 
volimie may be measured approximately and recorded, if the 
area so affected is located so as to permit of its being largely 


enclosed in a suitable container. Such containers of various 
adapted shapes are termed plethysmographs when used 
externally as when enclosing a forearm, or oncometers when 
used to enclose some internal organ like a loop of intestine. 


The normal regulation of the vasomotor apparatus is 
not well deciphered as yet. Besides the adjustment reflexes 
stimulated by impulses coming from sundry sensory areas, 
there are several factors which can exert widely A^arying 
influences. The suprarenal gland provides a secretion that 
produces a powerful though fleeting vasoconstriction when it 
is injected experimentally into the blood, but just how much 
of this is normally escaping into the blood is problematical; 
experiments by Cannon tend to indicate that the release of 
the secretion from the gland into the blood is accelerated 
by emotional excitement, protopathic sensory stimuli, and 
perhaps by various chemical substances in the blood. The 
internal secretion of the infundibular portion of the pituitary 
body also manifests a vasoconstrictor effect when injected 
into the blood stream; but how much of this is in the blood 
normally, or what factors may accelerate its release into the 
blood is unknown. The presence of weak acids produces a 
local vasodilatation of the arterioles; and this may explain 
in part the increased blood supply to muscles during their 
functional activity. It may well be, also, that variations 
of the mineral constituents of the blood have an effect on 
the vasomotor centers, or that the gaseous constitution of the 
blood has a local effect on the nerve terminals to the vascular 


All the viscera except the heart and lungs have some vaso- 
motor supply; all glands, mucosa, and integument are abun- 
dantly supplied with both vasoconstrictor and vasodilator 
fibers. No vasomotor supply has been demonstrated to 


the brain; it would seem that the intracranial blood-pressure 
is largely adjusted by compensating variations of pressure 
in other parts of the body, though some local adjustments 
are also possible through the balancing action of the cerebro- 
spinal fluid. If intracranial pressure rises in the bloodvessels 
through bodily vasoconstriction, back pressure of the cerebro- 
spinal fluid on the intracranial bloodvessels soon offsets it; 
if the arterial pressure falls too low, the resulting cerebral 
anemia irritates the vasconstrictor center and thus induces 
a restoration to the normal. 

As has been indicated previously, there is a vascular 
dilatation in the muscles whenever they are functionally 
active. There is some experimental evidence indicating 
that vasodilator fibers are supplied to the arteries of the 
muscles; but much of the augmented bloodflow may be due 
to the acid products of katabolism. 

There is also some limited evidence indicating that there 
may be some vasoconstrictir nerves going to the large veins, 
especially to the portal vein. 


The function of the blood is that of a general conveyor. 
(a) It carries foodstuffs to the tissues. 
(6) It bears waste products from the tissues to the emunc- 

(c) It carries oxygen from the lungs to the tissues. 

(d) It conveys carbon dioxide from the tissues to the lungs. 

(e) It transmits kinases, internal secretions, and other 
vital substances from their places of origin to their areas of 

(/) It serves to equalize temperatures and osmotic pres- 

These several functions of the blood are discussed in part 
incidentally to the various structures involved ; in this chapter 
more particular attention will be given to the constitution 
of the blood, and the various phenomena it manifests. 

Quantity.— The total quantity of blood in the body, as 
determined by Bischoff from two guillotined criminals, is 
about 7 per cent of the body weight. Some estimations as 
made from a computation of the amount of carbon monoxide 
displacement of oxygen in the blood indicates a ratio of 
blood to body weight as low as 5 per cent; but the higher 
figure is probably nearer correct. 

Specific Gravity.— The average specific gravity of the blood, 
as determined by the relative buoyancy of a drop of blood in a 
liquid of known specific gravity, is about 1.055. However, 
the normal varies greatly among individual, and in relation 
to age and sex; also a given norm falls during the day and 
rises during the night, increases after exercise and diminishes 
after meals. 




The blood is an aqueous liquid containing in solution some 
gases, many salts, and extractives; and holding in flotation 
a vast number of organized bodies, besides enzymes, protein 
compounds, secretins and special substances. The organized 
bodies are the red and white corpuscles; if these corpuscles 
are removed from the blood, the liquid remaining is pale 
yellow in color, and is called the blood plasma. Following 
is the 











21.0 in arteries 

Gases ^ 

Carbon dioxide 
^ Nitrogen 




Proteins < 








Fatty acid 



Extractives • 















f Chloride 



Sodium < 




Potassium < 











Gases.— Concerning the gases in the blood, consideration 
of oxygen and carbon dioxide is given under the discussion 
concerning the blood corpuscles (see infra). Nitrogen is 
present in constant volume at constant atmospheric pressures, 
and amounts thus to about 2 per cent of the blood; its pres- 
ence serves no other purpose than that of a diluent of the air 


breathed in. Present in the blood are also minute traces of 
the rare atmospheric gases, but they are not in quantities 
that admit of study. 


Fibrinogen.— Fihrinogen is a complex protein belonging 
to the globulin group; it is supposedly formed in the liver. 
Its most apparent function, and probably its most important, 
is the formation, under specific circumstances, of fibrin with 
the resultant local production of blood clot. 

Para^/o62^/m.— Paraglobulin is a protein whose origin and 
purpose are unknown; it amounts to about 2.8 per cent of the 
total proteins. 

Serum-albumin.— SeruYn-alhumin is assumedly derived 
from the proteins in the food, and is used to replace the pro- 
tein waste in tissues. 

Nucleo-albumin.— Nucleo-alhuinin is probably derived 
from the food nucleins. 

Red Blood Corpuscles.— The red blood corpuscles are minute, 
circular, biconcave disks, measuring on their face about 7.7 
microns (= 0.0077 mm.). The reddish color, which varies 
from the crimson-scarlet of arterial blood to the dark crimson 
of venous blood, is due to the oxyhemoglobin. The number 
of red blood corpuscles in the blood is about 5 million per 
cubic millimeter in the male, and about 4J million in the 
female, though the amount varies normally within fairly 
wide limits. The total amount is relatively greatest at birth, 
but it steadily decreases thereafter; it is greater before than 
after meals; it increases at the menstrual period, and decreases 
during pregnancy; the percentage of hemoglobin is said to 
increase in ascending to higher latitudes, in about the ratio of 
10 per cent for every 2000 feet ascent. 

The red blood corpuscles are formed in the red marrow of 
bones as erythroblasts which lose their nuclei before entering 
the blood stream. It has been estimated, from rather incon- 
clusive data, that the life of a red corpuscle in the blood 
stream is not over ten days; after that time it disintegrates, 
its stroma disappears, most of its iron content is retained in 
the system, but its hemoglobin is excreted as bile pigments 


by the liver. The chief function of the red blood corpuscles 
is to carry oxygen from the lungs to the tissues; its ability 
to do this is due to the presence within the corpuscles of the 
substance hemoglobin which is able to form with oxygen a 
loose chemical combination. 

Hemoglobin.— Yievcioglohm forms about 32 per cent of the 
weight of the red corpuscle, but in just what form it exists 
is unknown. It is a compound of hematin (4 per cent) with a 
protein (94 per cent) ; the hematin is the substance containing 
the iron. It has been estimated that in the adult male there 
are about 14 gm. of hemoglobin in every 100 gm. of blood; 
this makes the total amount in the blood of a man of average 
weight about 600 gm. This total amount is distributed among 
some 25 trillion corpuscles whose combined surface area is 
approximately 3200 square meters all of which area is 
apparently available for absorption of oxygen as the cor- 
puscles are streaming single file through the lung capillaries. 

When the oxygen passes into the corpuscle it forms with 
the hemoglobin, in the proportion of 1 gm. hemoglobin to 
0.0019 gm. of oxygen, a loose chemical compound termed 
oxyhemoglobin. The oxygen in this combination is released 
whenever the oxygen pressure in an adjoining medium is 
less than that in the corpuscle. It is a curious fact that 
though the hemoglobin in the corpuscle may be saturated 
with oxygen it is yet able to pick up carbon dioxide as though 
no oxygen were present; but the reverse possibility is said 
not to obtain. The ability of the oxygen to combine with 
the hemoglobin is due to the presence of the iron in the 
corpuscle; it is said that each atom of iron present is able to 
pick up one molecule of oxygen. 

The relative amount of hemoglobin present is usually 
determined by comparing a drop of blood (either in a per- 
centage solution or on filter paper) with a known standard 
of color tints, on a scale ranging down from 100 to 0. The 
standard for venous blood at 100 may be made by compound- 
ing on the color disk 67 parts of best English vermilion, and 
10 parts of ultramarine, with 23 parts of best lampblack. 

Combination of hemoglobin solutions with the various 
atmospheric gases give characteristic spectroscopic appear- 


ances. Inasmuch as the appearance varies according to 
the percentage strength of the blood solution, and the rel- 
ative thickness of the layer examined, it will be well to 
arbitrarily select a solution of about 0.3 per cent strength, 
contained in a test-tube 1 cm. in diameter. 

White Blood Corpuscles.— The number of white blood cor- 
puscles in a cubic milliliter of blood is about 9000; though 
this amount increases during digestion, during pregnancy, 
and after exercise. Many varieties of white blood corpuscles 
are described in textbooks of histology, but very little is 
known of the particular functions of most of these varieties. 
They all seem to have the power of amoeboid motion, whether 
they chance to be in the bloodvessels, in the vessel walls, or 
in the lymph spaces. From the way in which they seem to 
swarm to an injured or infected area it is assumed that in 
some way they counteract inflammatory and deteriorative 
processes, possibly by destroying bacteria and by then remov- 
ing the detritus from the affected area. Also it is thought 
they aid somewhat in the absorption of fats and peptones 
from the bowel. The origin of leukocytes is bone-marrow 
and lymph glands. 

Blood Platelets.— Besides the white and red corpuscles 
there sometimes exist in shed blood various colorless disk- 
shaped bodies called blood platelets. Demonstration of these 
bodies requires special treatment of the blood, so their pres- 
ence long escaped observation. In some preparations they 
have been found to the number of 250,000 to the cubic milli- 
meter. Their origin or fate is unknown though they probably 
are concerned in the coagulation of the blood; it is very 
doubtful, according to Starling, if they exist as such in cir- 
culating blood; even in shed blood their condition is very 
transitory unless fixed by suitable preservatives. 


As is well known, blood coming from an injured area, or 
received into a vessel from a severed artery or vein, normally 
forms a gelatinous mass called a clot. If this clot is examined 
under the ultra-microscope it shows blood corpuscles entan- 


gled in a fine interlacing mesh called ./z6ri?i. Much study and 
experimentation has shown that the fibrin threads are 
derived from a combination of the fibrinogen of the blood 
with another protein substance termed thrombin. However, 
this thrombin does not exist in the blood as such but in the 
form of an inactive antecedent termed 'prothrombin. Just 
what converts prothrombin into thrombin is not known, 
although it is known that the presence of calcium is an essen- 
tial factor in the process. It is assumed that injured tissue 
cells, or disintegrating blood plates, furnish an activating 
substance that initiates the conversion of prothrombin into 
thrombin, and that the thrombin then unites with the fibrin- 
ogen in a physico-chemical combination to form fibrin. An 
additional assumption is that the blood normally contains 
an antagonistic agent, termed antithrombin, which serves 
to prevent the formation of fibrin within the bloodvessels, 
and this serves to maintain the normal fluidity of the blood 
stream. (A related substance may be isolated from the sali- 
vary glands of the common leech.) Prothrombin may be 
converted into thrombin by the presence in the blood of 
macroscopic foreign particles, or by the exudate from injured 
endothelium; from the localized clot thus formed, termed a 
thrombus, detached particles, called emboli, may be swept 
into the general circulation and borne on until they reach 
an arteriole of too small caliber to permit passage but whose 
lumen they may absolutely block; such an obstruction cuts 
off the blood supply to the part lying beyond, with possible 
very grave results. 

In case of severe hemorrhage regeneration proceeds rapidly 
as to volume, but very much more slowly in regard to the 
corpuscular elements, especially the red corpuscles. Regen- 
eration of volume takes place by osmosis from the tissues; 
it may be greatly hastened by subcutaneous or rectal injec- 
tions of normal salt solutions. Regeneration of the other 
elements takes place by means of new creations of the cor- 
puscular elements, and abstraction of other elements from 
sources of supply. 

The reaction of the blood is very weakly alkaline; the 
hydrogen-ion concentration is less than that of a neutral 


fluid like water. This reaction is maintained with remarkable 
constancy, despite the many possible influences that may be 
physiologically present tending to upset the standard con- 
dition. This continuing neutrality of the blood in the pres- 
ence of adverse factors is due to three salts present in the 
blood: A weak acid salt, monosodium phosphate, and two 
alkaline salts, disodium phosphate and sodium bicarbonate. 
These three salts in the blood together make a buffer solution 
that tends to neutralize at once the addition to the blood of 
any alkali, as from the bowel during digestion, or the addition 
of any acid, as from the muscles during activity, or from the 
liver or from the bowels. 


One of the functions of living cells is self-protection against 
hostile invading cells or their toxins or the poison of dead 
cells. Bacteria are the principal enemy; protection is required 
against them and against their poisons whether intracellular 
or extracellular. But besides bacterial poison, dead cells of 
protein origin, or the animal or vegetable decomposition 
products of protein katabolism, are all extremely potent in 
toxicity; not infrequently such poisons overwhelm the body 
cells before resistance can be adequately organized. Just 
what may be the nature of such resistance is obscure, though 
many experiments indicate that both the serum of the blood 
and the stroma of the blood corpuscles are intimately con- 
cerned in the development of immunity. Experiments with 
animals show that repeated injections at suitable intervals 
of regular increments of certain toxins produce in time the 
development of a high grade of immunity specific for that 
particular toxin; and that the immunity thus developed may 
be transferred to another animal by means of the transfer 
of some of the serum of the immunized animal into the blood 
stream of the second animal. From these experiments it is 
assumed that the presence of minute amounts of toxin in 
the blood results in the production of a specific neutralizing 
agent capable of rendering innocuous that particular toxin; 
and, in the case of bacteria, the further achievement of ren- 


dering unfavoring the tissue on which that particular set 
of germs has thus far been developing. But just what may 
be the nature of this immunizing agent, or in what manner 
it may act, are problems yet awaiting solution. 


The individual cells of the body have each a definite met- 
abolism. Each absorbs nutrient material from the blood, 
reconstructs this material into new compounds, discards the 
unutilizable, and excretes the waste resulting from its meta- 
bolic activities. In order that these several functions may 
be carried on unhampered it is essential that each cell 
shall be furnished with an ample supply of assimilable mate- 
rial and be assured of the rapid removal of its own products 
of katabolism. An agent for such service is furnished by the 
lymph; this is a thin clear liquid that bathes every cell more 
or less completely. This lymph is derived from the blood, 
and makes its way from the capillaries into the intercellular 
spaces by transuding through the endothelial cells of the 
capillaries, a process of filtration, diffusion and osmosis, with 
possibly some selective absorption action of the cells them- 

This transudative process apparently acts here as in other 
related conditions. If the relative osmotic pressure is higher 
in the lymph spaces than in the capillaries the current of 
flow will be from the capillaries into the lymph spaces; this 
condition seems fairly constant. Crystalloids, protein prod- 
ucts, and difi^usible colloids pass through the capillares as 
solutes from the blood plasma; this resulting extra vascular 
liquid constitutes the intercellular lymph. From this lymph 
the cells take up their nourishment, and to it they give their 
waste. The lymph solution containing the katabolic waste 
is taken up in part by the blood capillaries, and in part by 
the lymph capillary radicles; these latter convey the lymph 
into the smaller lymphatics, and then it goes into the larger 
lymphatics and so on until it is again thrust back into the 
blood stream. 

There is not a constant pressure in the intercellular lymph 


spaces. The tissue elements take up the major portion of the 
lymph, and there is a steady flow of lymph from the tissue 
elements back into the capillaries. There is also an indeter- 
minate flow from the lymph spaces into the lymph capillaries, 
varying in different tissues and because of many changes of 
relative pressure. Lymph flow is scanty in the limbs, but 
relatively abundant from the liver and intestines; these 
variations are due in part to relative permeability, but more 
to the rapid functioning of the parts involved. In any case 
the nutritive and eliminative needs of a tissue are what seem 
to determine the lymph flow of that particular region. 

The flow of lymph along the capillaries and lymphatics 
is maintained largely by the pressure in the lymph spaces, 
which pressure depends finally on the more fundamental 
pressure in the arteries. Accessory factors assisting the prog- 
ress of the lymph onward are: (a) Peristaltic movements 
and rhythmic oscillations of the intestines; {h) the aspiratory 
action of the thorax during inspiration, whereby the pressure 
in both the subclavian vein and the thoracic duct is lowered ; 
(c) compression by the skeletal muscles. 

The lymph nodes and glands, scattered so plentifully along 
the course of the lymphatic vessels, constitute a possible 
source of the lymphocytes; through their reticulated tissue, 
they also serve as strainers and filters of the on-streaming 


Rous and Turner: Living Erythrocytes in vitro, Jour. Exp. Med., 1916, 
23 , 219, 239. 

Rous and Robertson: Destruction of Erythrocytes in the Body, Jour. 
Exp. Med., 1917, 25, 651, 665. 

Stewart: Mechanism of Hemolysis, Jour. Pharmacol., 1909, 1, 49. 

Kanthack and Hardy: Wandering Cells of Mammalia, Jour. Physiol., 
1894, 17, 81. 

Lee and Minot: Significance of Blood Platelets, Jour. Am. Med. Assn., 
1917, p. 1211. 

Cullen: Reaction of Blood, Jour. Biol. Chem., 1917, 30, 369. 

Henderson and Black: Regulation of Blood Reaction, Am. Jour. Phys., 
1908, 21, 420. 

Howell: Blood Coagulation, Am. Jour. Phys., 1911, 29, 187. 

Whipple: Origin of Fibrinogen, Am. Jour. Phys., 1914, 33, 50. 

Minot and Denny: Prothrombin and Antithrombin in Coagulation, Arch. 
Int. Med., 1916, 17, 101. 

Auer and Robinson: Anaphylactic Shock, Jour. Exp. Med., 1913, 18, 450. 


Wiggers: Events of the Auricular Systole, Am. Jour. Phys., 1916, 42, 141. 

Wiggers and Deans: Nature and Time Relations of Heart Sounds, Am. 
Jour. Phys., 1917, 42, 476. 

Magrath and Kennedy: Coronary Circulation and Heart Beat, Jour. 
Exp. Med., 1897, 2, 13. 

Porter: Influence of Heart Beat on Coronary Flow, Am. Jour, Phys., 
vol 1, p. 145. 

MacWilliams: Conduction of Pulse Wave, Heart, 1912, 4, 393. 

Dawson: Arterial Blood-pressure at Different Points, Am. Jour. Phys., 
1906, 15, 244. 

MacLeod: Measurement of Blood-pressure in Man, Jour. Lab. and Clin. 
Med., 1915, 1, 62. 

Murlin and Greer: Relation of Heart Rate to Respiratory Mechanism, 
Am. Jour. Phys., 1914, 34, 368. 

Eyster and Meek: Location of Pace Maker, Am, Jour, Phys., 1914, 34, 

Martin: Ventricular Tonus and Cause of Heart Beat, Am, Jour, Phys. 
1912, 30, 182. 

Hunt: Relation of Accelerator to Inhibitor Nerves, Am. Jour. Phys., 
1899, 2, 395. 

Martin: Blood Salts and Heart Action, Am. Jour. Phys., 1913, 32, 165. 

Porter and Turner: Vasomotor Mechanism, Am. Jour. Phys,, 1915, 39, 

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Phys., 1910, 27, 276. 

Wiggers: The Circulation in Health and Disease. 1915, 


The structures concerned more particularly with respira- 
tion are the nose and nasal passages; the pharynx, larynx and 
trachea; the thorax with some of its contained viscera; bron- 
chi, lungs and pleurae; and the various muscles which serve 
to increase or decrease the lung spaces. 

The nose and its passages serve as a means for warming 
and moistening the inspired air. The anterior nares, sur- 
rounding the vestibule, can be considerably broadened by 
the action of the dilator muscles; this would afford freer 
entrance of air in urgency of respiration. Above the superior 
concha is the area concerned with the sense of smell (see p. 
232). Distributed over that portion of the nasal passages 
below the superior concha, and especially over the whole 
of the inferior concha, is a modified mucous membrane under- 
laid with cavernous tissue. The engorgement and emptying 
of this cavernous tissue are largely governed by reflexes 
arising from variations of temperature and humidity; with 
low temperatures the engorgement is considerable, as it is 
also with high dry temperatures, but when the air is both 
warm and moist there is minimal filling of these tissues. The 
tissue becomes highly engorged when markedly irritated by 
extraneous substances, or by the germs that accompanv 

Because of the position of the vestibule of the nose, inspired 
air circulates through all the nasal passages, including the 
olfactory portion; but because of the conformation of the 
roof of the nasopharynx, expired air is deflected so much 
toward the outlet that usually none of it passes through the 
olfactory portion, and as a result odors in the expired breath 
are rarely perceptible to the subject. 


The nasopharynx and the pharynx assist in the warming 
and moistening of the inspired air, though to a less extent 
than the nasal passages that lie more anterior. 

The amount of air passing through the larynx during a 
given respiration may be considerably modified by the action 
of those muscles that control the upper laryngeal orifice 
(the rima gloUidis), In conditions of difficult breathing 
(termed dyspnea) the orifice of the larynx is stretched open 
as wide as may be possible under the circumstances. This 
orifice serves two functions : that concerned with the passage 
of simple respiratory air, and that concerned with the use 
of that air in the production of sound (see p. 252). This 
opening into the larynx lies just behind the base of the tongue 
and just anterior to the opening into the esophagus. 

From the larynx passes to the lungs a fibrocartilaginous 
tube, the trachea, which bifurcates into distributory tubes, 
the bronchi. These tubes are kept open by means of car- 
tilaginous rings, in the trachea and larger bronchi, and by 
cartilaginous plates, in the lesser bronchi and bronchioles; 
the cartilage disappears when the bronchioles reach a diam- 
eter of about 1 mm. Variations of the caliber of the lesser 
tubes are possible because of the presence of involuntary 
muscle in the walls of the bronchioles; the smaller bronchioles 
not possessing any cartilaginous plates, are entirely sur- 
rounded by muscle; so powerful is this muscle as to be able 
to completely close the lumen of the tube in some cases of 
spasmodic irritation. The unit structure of the lungs is 
composed of the atria and alveoli in which the bronchioles 
terminate; surrounding these alveoli are the capillaries of the 
pulmonic bloodvessels; through the walls of the alveoli take 
place those exchanges of gases that constitute respiration. 
It has been estimated that the entire surface area of the 
atria is equal to 90 square meters. 

The elastic osseomyocartilaginous thorax is a closed cavity 
in which rest the two large membranous sacs called the lungs 
(Fig. 30); but though this thoracic cavity is a closed space, 
yet the enclosed lungs communicate freely with the outside 
air through the bronchi, trachea, larynx, and nasopharyngeal 
passages; as a consequence atmospheric air pressure keeps 



the lungs expanded until they occupy the entire available 
cavity of the thorax. If the thoracic cavity enlarges in any 
of its diameters, then the contained lung sacs enlarge to the 
same degree; on this constant relationship, depends the 


Fig. 30.— Front view of heart and lungs. (Gray.) 

mechanical mechanism of breathing; for as the thorax enlarges, 
air rushes into the lungs to occupy the enlarged space, and 
as the thoracic cavity diminishes in cubical area, air is forced 
out of the lungs. 



The lower opening of the osseous cage of the thorax is 
closed in by a muscle sheet of arch-like contour, the diaphragm 
(Fig. 31). When this muscle contracts it produces a flatten- 
ing of the arch, and this results in an increase of the vertical 
diameter of the thorax. Accessory muscles are attached to 
the edges of the ribs; and when these contract, they lift up 
these edges and so enlarge somewhat the lateral diameter of 
the thorax; yet other' accessory muscles are so attached that 

Fig. 31. — The diaphragm, viewed from in front. (Testut.) 

when they contract they make the obliquely-placed ribs 
more nearly horizontal, and so enlarge somewhat the antero- 
posterior diameter of the thorax; but the diaphragm is the 
chief muscle for increasing the capacity of the thoracic cavity. 
When the diaphragm contracts it tends momentarily toward 
the production of a diminished air pressure, but the tendency 
toward the disturbance of equilibrium is compensated by 
the inrush of atmospheric air; this inrush constitutes inspira- 
tion. When the muscle activity that produces inspiration 


ceases, the thorax and contained lungs return, through their 
own elasticity, to their former position and relationship; 
this return to the previous passive position constitutes 

When the movements of respiration are within normal 
limits, the type of breathing resulting is termed eupnea . When 
the breathing becomes forced and labored, and the accessory 
muscles are called into action, the activity is spoken of as 
dyspnea. It may be well to note that in this latter type of 
breathing, the muscles which open wider the vocal cords, and 
the muscles of the nasopharynx and nares, are all called 
into action. In quiet breathing, where there is no constraint 
of the abdomen and lower thorax, the diaphragm is the 
muscle chiefly active, followed by more or less action of the 
levatores costarum and the external intercostals; this is termed 
the abdominal type of respiration. Where this normal activ- 
ity is restrained, as in the case of those who gird themselves 
tightly, the principal activity is by the levatores costarum 
muscles, aided by the external intercostals; this is termed the 
costal or thoracic type of breathing. The abdominal t^-pe 
ventilates the lungs more completely, besides accelerating 
movements in the bile ducts and in the infra-abdominal 
vessels. The most healthful form of breathing is where the 
two forms are adequately combined, thereby ventilating 
the entire lung alveoli most thoroughly. 

Several terms are used by physiologists to denominate the 
varying quantities of air breathed under different conditions. 
Tidal air indicates the amount breathed in (or out) in a nor- 
mal respiration; the average amount of tidal air is about 
500 cc. Complemental air represents the excess of air one 
can inhale over and above the normal inspiration; this 
amounts to about 1600 cc. Supplemental air is the excess 
amount one can force out of the lungs after the completion 
of a normal expiration; this also amounts to about 1600 cc. 
Therefore, the sum of all these, from the deepest inspiration 
to the completest expiration, may be termed the vital capacity. 
But even after the most forcible expiration, there must 
remain some air in the lungs, and atmospheric pressure keeps 
that much filled; this remaining portion, termed residual air, 


is determined in animals by collecting the air forced out 
when the lungs collapse at the time of opening the chest; 
in man it is estimated this residual air amounts to about 
1000 cc. This makes the normal supply of the lungs, the 
amount that must be aerated at each breath, equal to about 
2600 cc. There must be very rapid diffusion, therefore, if 
the tidal air of 500 cc. is to adequately ventilate the 2600 cc. 
already contained within the bronchi and alveoli. 


The descent of the diaphragm, or the elevation of the ribs 
and sternum, tends to produce a fleeting rarefaction of the 
air in the pulmonary spaces, even though this tendency is 
promptly overcome by the inrush of atmospheric air. The 
degree of this rarefaction amounts to about — 9 mm. of 
water, but the degree will be necessarily altered by the rapid- 
ity and extent of the respiratory effort, and by the relative 
ease or difficulty with which outside air enters the respira- 
tory passages. At the end of inspiration, the elastic lungs 
compress the contained air with a force equal to about 
+ 7 mm. water. 

The elasticity of the lung tissue tends with considerable 
force to draw the surface of the lung from the intrathoracic 
wall, a tendency which is largely offset by the atmospheric 
pressure exerted through the pulmonary areas; yet this 
traction elasticity actually produces a negative pressure, 
in the pleural spaces at the end of inspiration, equal to about 
— 7 mm. Hg., and equal to about — 3.02 mm. Hg. at the end 
of expiration. Any interference with the ingress of air 
increases this negative pressure; conversely, any interference 
with the egress of air from the lungs will decrease this nega- 
tive pressure. If, by unfortunate chance, atmospheric air 
enters the potential intrathoracic area, the lung of that side 

All the structures in the mediastinal spaces are subject 
to all the effects of this negative intrathoracic pressure, espe- 
cially the great veins and the right auricle; this undoubtedly 


has considerable influence in facilitating the flow of blood 
in the vencB cavce. Observations show that there is an increase 
of this flow, both in velocity and volume, during inspiration 
while the negative pressure is increasing. This effect on 
thoracic venous circulation is sometimes referred to as the 
aspiratory action of the thorax; it acts coincidentally with the 
increased intra-abdominal pressure brought about by the 
descent of the diaphragm. 

Physical Changes in Respiration.— Whatever may be the 
temperature of the inspired air, the expired air is warmed to 
nearly the temperature of the body; it is also nearly satu- 
rated with water vapor. It has long been contended that the 
expired air also contains a noxious animal exhalation to which 
is due the ill-effects arising from remaining in a badly-venti- 
lated room; this claim has been denied by other observers, 
and at present remains an open question, having little or no 
supporting evidence. 

Chemical Changes in Respiration.— Under normal conditions 
of breathing, respired air gains 4.34 volumes of carbon dioxide 
with traces of hydrogen and methane, and loses 4.94 volumes 
of oxygen. The excess of oxygen loss over carbon dioxide 
gain is compensated by oxygen used up in oxidations of 
food and hydrogen. Repeated examinations show that 
arterial blood contains, on an average, 20 volumes per cent 
of oxygen and 38 volumes per cent of carbon dioxide. These 
amounts necessarily vary with the state of activity of the 
organs, or part examined, as increased activity involves 
heightened oxidations; the existing temperature at the time 
of examination will also influence the result. 

As learned in physics, the oxygen in the air is under a 
relative pressure of 152 mm. Hg., since oxygen composes 
about one-fifth of atmospheric air. In the alveoli, however, 
because of the great increase in the actual amount of carbon 
dioxide, and the decrease in percentage of oxygen, the oxygen 
tension is reduced to 107.2 mm.; and this is further reduced 
by the water vapor to about 100 mm. In alveolar air, then, 
the oxygen pressure has a tension of about 100 mm. Hg. 
But this alveolar air is practically in contact with the stream 
of blood passing constantly on the other side of the extremely 


thin (0.004 mm.) endothelium, a tissue that presents prac- 
tically no obstacle to diffusion of gas. Now since gas under 
a higher tension tends to flow into a medium where the tension 
is lower— just as water seeks its level— so in the alveoli the 
gas under greater tension will flow in the direction of less 
resistance. And since in the venous blood flowing into the 
interalveolar spaces the oxygen is under a tension of only 
37.6 mm. Hg., diffusion must take place from the alveoli 
into the blood. This is demonstrated by comparative esti- 
mations wherein it is found that venous blood coming to the 
lungs contains about 12 volumes per cent of oxygen, while 
that passing from the lungs contains nearly 20 volumes per 

In the same way it has been found that the venous blood 
coming to the lungs contains 45 volumes per cent of carbon 
dioxide, under a relative pressure of 46 mm. Hg. ; and, since 
the carbon dioxide tension in the alveoli is but about 40 mm. 
Hg., diffusion must take place from within outward. And 
as it may be ascertained that the arterial blood going from 
the lungs has but 38 volumes per cent carbon dioxide, there 
has been a diffusion loss of this gas of approximately 7 per 
cent. It has been estimated that the diffusion capacity of 
the alveolar membrane is equal to over 6000 cc. of oxygen 
a minute, whereas the actual requirements vary from about 
300 cc. when at rest to about 3000 cc. during violent exertion. 

The total amount of oxygen absorbed in twenty-four hours 
has been estimated as approximately 700 gm. (347 cc. per 
kilo per hour) ; and the amount of carbon dioxide discharged 
in the same time as approximately 800 gm. (the average 
equals 250 cc. per kilo per hour, increasing 20 per cent dur- 
ing waking hours) . Since only about 72 per cent of the carbon 
dioxide is oxygen, there must be about 120 gm. more of 
oxygen absorbed in a day than is given off in the form of 
carbon dioxide. It is believed that the balance is largely 
used up in the oxidation of proteins and fats. Thus, on a 
pure carbohydrate diet, the discharge of oxygen in the carbon 
dioxide should just about equal the amount of oyxgen 
absorbed; this equality is not found when the subject is fed 
on a mixed diet. The ratio of oxygen absorbed to carbon 


dioxide discharged is often spoken of as the respiratory 
quotient; its determination is occasionally important in esti- 
mating the nutritional changes taking place in the body. 

Condition of the Gases in the Blood. —In the blood the greater 
part of the oxygen is held in a loose chemical combination 
with the hemoglobin of the red blood corpuscles, a combina- 
tion rapidly broken up when the oxygen pressure of any 
tissue through which the blood is flowing is at 70 mm. or 
below, and correspondingly less rapidly at points of approach- 
ing equality of tensions. Besides the oxygen in combination, 
there is also some oxygen dissolved in the plasma of the blood ; 
but it is doubtful if the plasma will take into solution 
much more than 0.4 per cent unless the oxygen tension in the 
alveoli rises considerably above its usual normal of about 
100 mm. Hg. 

The carbon dioxide is more extensively distributed in the 
blood components. Nearly 4.75 per cent of the total carbon 
dioxide present in arterial blood (40 volumes per cent) is in 
physical solution in the plasma; about 47 per cent of the 
total is held as sodium bicarbonate (17 per cent of which is 
in the corpuscles and 30 per cent in the plasma); and the 
balance, 48.25 per cent, is held in organic combination (of 
which 18.75 per cent is in the corpuscles and 29.5 per cent 
in the plasma). This organic combination is assumed to be 
with proteins which, in such a case would act as weak acids 
capable of picking up the free carbon dioxide in the tissues, 
then to release it again under the stress of the lower tension 
prevailing in the lungs. (It must be admitted this theory 
is not entirely satisfactory, though it seems the best avail- 
able at present.) 

Role of the Nitrogen.— So far as has been ascertained, the 
nitrogen of the air serves no other physiological utility than 
mere dilution of the oxygen. It seems to be absorbed some- 
what into the blood where it is held in simple solution; but it 
does not seem to exert any particular influence. 

Exchange of Gases in the Tissues.— Repeated examination 
of the tissues show that oxygen is present at a pressure very 
close to zero, since whatever is present is in chemical com- 
bination; but the carbon dioxide is under a tension of 50 to 


70 mm. Hg., owing to its constant formation. Therefore, 
when the blood enters the capillaries with an oxygen tension 
of 100 mm. Hg., and a carbon dioxide tension of but 40 mm. 
Hg., there ensues an extremely rapid diffusion of gases, each 
gas moving of course in the direction of less tension. At this 
point the blood loses about 35 per cent of its oxygen, and 
increases its carbon dioxide about 16 per cent. The presence 
of carbon dioxide under high tension in the tissues has been 
found experimentally to facilitate the diffusion of the oxygen. 
The gases are transmitted from the blood corpuscles to the 
tissues, and from the tissues to the blood stream, by the 
plasma of the blood and by the intercellular lymph, both of 
which here serve as intermediaries. 

Respiration proceeds regularly throughout life, the inspir- 
atory muscles receiving contraction impulses continually 
at an average rate in the adult of 18 a minute. This definite- 
ness of action has been shown to be due to a rhythmic activity 
of the respiratory center in the medulla, from which center 
action currents proceed with clock-like regularity. This 
rhythmic activity may be temporarily suspended by volun- 
tary control of the respiratory muscles, but in a short time 
the urgency of centric demands supersedes the intentions 
of the will, and the inspiratory muscles resume their activity. 
Other factors, like sensory or emotional reflexes may momen- 
tarily interrupt the orderly sequence, but for a brief time 

Many experiments indicate that the rhythmicity of the 
respiratory center is governed by the gaseous condition of the 
blood. If any condition, voluntary or otherwise, produces a 
change in the venosity of the blood supplying the respiratory 
center, there is an immediate change in that center's activity. 
If the blood going to the center carries relatively more oxygen 
than the normal, then the center lessens its activity, either 
in force or frequency or in both; if, on the other hand, this 
afferent blood contains a relative excess of carbon dioxide, 
then the center's activity increases proportionally. Now is 
this result due normally to lessened oxygen or to increased 
carbon dioxide? The major evidence favors the view that 
carbon dioxide is the active factor in stimulating the respir- 


atory center. If the carbon dioxide tension in the blood falls 
below about 25 mm. Hg. the activity of the center ceases, 
and respiratory movements come to an end; but, since the 
acid products of metabolism have to be oxidized, the center's 
activity will be toxically irritated whenever the supply of 
ox}^gen falls below local katabolic requirements. In the 
opposite direction, successive increments of carbon dioxide 
tension are followed by proportionate increases in the center's 

The first respiratory movement of the newly-born child 
is due in part to sensory reflexes from the skin, and in part 
to increasing venosity of the blood going to the center. 


Sharp sensory stimuli, like a dash of cold water, or a sudden 
pain, and strong emotions usually temporarily inhibit respir- 
atory action following a quick, short inspiratory gasp; this 
is usually followed soon by rapid, shallow, possibly quivering, 
respirations. The first phenomenon is probably a muscle 
reflex; the second is a nervous disturbance affecting the cor- 
relativity of action, with, especially in fright, a possible 
influence from some psychically-induced toxins in the blood. 
(Such toxins may tentatively be assumed to be imperfectly 
metamorphosed products of cellular activity prematurely 
disjoined in some way by means of the nervous shock. If a 
nervous impulse can produce muscle contraction, surely 
powerful emotional impulses thrown into the sympathetic 
system can easily upset normal metabolism.) Experimental 
stimulation of sensory nerve trunks is sometimes followed by 
more rapid and deeper inspirations. 

Certain experiments make it seem probable that the present 
condition of the lungs has some influence on the respiratory 
center. On expansion of the lungs, sensory fibers from the 
surfaces of the alveoli send influences that are inhibitory and 
which serve to check further inspiratory impulses from the 
center; furthermore, completion of the elastic recoil in expira- 
tion sets into action a series of nerve impulses that tend to 


excite the center to renewed activity. These impulses travel 
in the vagus nerve. 

Irritation of the mucosa of the nose, pharynx, larynx, 
and trachea set up influences that cause a transient cessa- 
tion of respiration by reflex contraction of the muscles of the 
pharynx, larynx and bronchioles. 

The normal oxygen pressure in the atmosphere, it will be 
recalled, is 152 mm. Hg. Reduction of this relative tension 
seems to produce no ill-effects until a pressure of about 75 
mm. Hg. is reached, at which point the blood is unable to 
take up adequate supplies for the needs of the tissues. This 
condition of inadequate oxygen supply to the blood is termed 
anoxemia. A drop in oxygen tension to 50 mm. Hg. is soon 
followed by death with convulsions. On the other hand, if 
the oxygen tension be raised, no injurious results ensue until 
the tension approaches 400 mm. Hg. when death with con- 
vulsions may ensue. What may be the cause of the fatal 
outcome in this latter case is a question not yet settled. 

It will be recalled that the normal tension of the carbon 
dioxide in alveolar air is approximately 35 mm. Hg.; when 
this tension falls to approximately 23 mm. Hg., respiration 
ceases from lack of centric stimulation; this condition is 
termed acapnia. Soon the accumulation of acid products 
will irritate the center to further temporary activity, but 
respirations soon cease again, and death will result if carbon 
dioxide stimulation of the center be not promptly forth- 
coming. On the other hand, if the carbon dioxide pressure 
be increased to an atmospheric content of 3 per cent (21 mm. 
Hg. instead of the normal 0.28 mm.), a noticeable hyper- 
pnea will result. If the atmospheric carbon dioxide tension 
approaches 10 to 12 per cent (72 to 86 mm.), there is disagree- 
able dyspnea. If the carbon dioxide tension rises to 40 per 
cent (atmospheric), death ensues without convulsions but 
with the appearance of general narcosis. Explanation of the 
fatal outcome is that it is due to actual poisoning of the nerve 

The effect of increased pressure of gases is especially 
noticeable with caisson laborers who work in atmospheric 
conditions where the pressure increases 1 atmosphere with 


every 35 feet descent; but very seldom is it necessary to use 
more than 2 to 3 atmospheres for this work even in submarine 
construction with the boring shield. Just as soon as men get 
accustomed to the increased pressure they apparently work 
without minding it, showing that this pressure is readily 
accepted by a quickly adaptable organism. Under such pres- 
sure, however, the several gases enter the plasma of the blood 
in a state of solution; and if the pressure is too suddenly 
released, as in too rapid decompression in returning to the 
outer air, the excess gases, especially the nitrogen, are freed 
from the plasma in the form of little bubbles, and these 
bubbles may readily block small capillaries, producing dis- 
tressing and even fatal results. 

Decreased pressure of gases is noticeable when climbing 
mountains, living in high altitudes, or ascending in air ships. 
The more prominent symptoms produced are headache, 
dizziness, and great physical weakness. Concerning the 
cause of these symptoms much discussion has arisen, some 
contending the suffering is due to anoxemia, others asserting 
that acapnia is the factor. There seems no doubt that the 
decrease in tension of each gas may have its particular effect. 
If one ascends a mountain 2000 meters, he is in an atmosphere 
where the pressure is only about two-thirds of what it was 
at the starting place; at this point the tension of the oxygen 
is such as to permit of but slight diffusion, while that of the 
carbon dioxide is such that diffusion is too rapid ; of these two, 
the lowered tension and slight diffusibility of the oxygen 
seems the more important. In addition to the mechanical 
impediments resulting from such reductions of surface 
pressure, there are also inevitable disturbances to pulmonary 
and circulatory equilibrium. 

Muscular activity has a direct augmentatory action both 
on the amplitude and rate of respiration, due to the increased 
demand for oxygen in the muscles, to the excess of carbon 
dioxide being given off, and to the rapid increase in the blood 
of the acid products of muscle metabolism. This increase 
amounts to 25 per cent, with moderate activity, ascending 
very rapidly as the work or exercise becomes more strenuous. 
An increase is also brought about indirectly by rises and falls 


of the temperature of the air, lower temperatures producing 
reflex increases of muscular activity, and higher temperatures 
tending in the opposite direction. Any endogenous increase 
in the body's temperature accelerates the activity of the 
respiratory center through heightening its irritability. 

Similar results ensue, both relatively and absolutely, as a 
direct result of age; the great activity of childhood and 
youth necessitating more rapid tissue respiration, while 
the diminished activity of later life demands less. In a like 
way, increased oxygenation is apparent during digestion, 
due in part to augmented muscle activity in the alimentary 
tract, and in part to food oxidation. 

Breath Sounds.— On listening over the trachea or bronchi 
there may be heard a soft rushing sound accompanying both 
inspiration and expiration. This sound is due to the passing 
of the air through the larger air tubes, and is not heard else- 
where in the normal chest. On listening beyond the bronchial 
area there may be heard a soft rustling sound during the 
terminal period of inspiration; this sound, it is thought, may 
be due to the rush of air from the atria into the infundibula, 
or possibly to a sudden dilation of the air vesicles, hence the 
term vesicular murmur; this sound is heard over healthy 
lungs only. 

The respirations in sleep are deeper and slower than in 
the waking condition, and are more costal in type, frequently 
show a slow oscillating periodicity, and are shorter and 
sharper in expiration. 

Coughing.— In coughing there is a forcible expiration due 
to sharp and sudden compression of the abdominal muscles, 
but the expiratory blast is held up by one or more momen- 
tary closures of the glottis; the glottic spasm is quickly 
overcome by the rapidly increasing pulmonic tension, and 
the air shoots out with strong expulsive force. Normally 
this act is a reflex from the larynx or bronchi, but it may be 
imitated at will. 

Sneezing.— Sneezing is much akin to coughing except that 
a reflex contraction of the isthmus fauci forces the blast of 
air through the nasal passages in which usually arises the 
provocative reflex, 


Hiccough.— Hiccough is somewhat the reverse of a cough. 
In this conditions there is an invohintary, semi-spasmodic 
descent of the diaphragm, and the rapidly in-rushing air 
is suddenly checked by a sharp sudden closure of the glottis. 
This act is believed to be a reflex from the stomach so far 
as the sudden movement of the diaphragm is concerned; 
the glottic accompaniment is not satisfactorily explained, 
but may be a reflex through the vagus. 

Sobbing.— Sobbing is mechanically a series of voluntary 
hiccoughs of weak intensity. A long inspiration is interrupted 
by several successive vibrating closures of the glottis. 

Snoring.— Snoring is a vibration of the soft palate between 
two currents of air, inspiratory or expiratory, one through 
the nose and the other through the mouth. The double 
current is not essential, however, as a relaxed soft palate 
will vibrate when a current of air rushes past either surface; 
many persons snore with the mouth closed. 

Sighing and Yawning.— Sighing and yawning are excep- 
tionally deep inspirations, the latter being usually accom- 
panied by stretching movements of the muscles of the throat 
and mandible. Each is probably a lung reflex. 

Pleurae. — The pleurae surrounding the lungs, and lining 
the thoracic cavity, serve as lubricating surfaces whereby 
the continual movements of the lungs against the thoracic 
walls may have the friction coefficient reduced to the abso- 
lute minimum. 

Artificial Respiration. — For keeping alive the spark of life it is 
sometimes necessary that the respiratory movements be main- 
tained artificially. To effect this result air must be drawn into 
the lungs and then forced out, and the process maintained with 
rhythmical frequency. Since it is impossible to utilize the 
diaphragm in artificial respiration, reliance must be placed 
on the costal mechanism. Forcible extension of the arms, 
through its traction effect on the rib muscles, everts and elevates 
the ribs thereby increasing the thoracic cavity in its lateral 
diameters and effecting an inspiratory movement of air. 
Compression of the lower costal area, the arms having been 
lowered, effects an expiratory movement of air. Rhythmical 
repetition of these two movements, at the rate of 18 to 20 


times a minute, as in the Sylvester method of artificial respira- 
tion, provides not infrequently a temporarily adequate sub- 
stitute for normal breathing; through such means many lives 
have been resuscitated. A method used with newly-born 
infants consists in alternate extreme extension and flexion of 
the body, respectively producing inspiration and expiration. 


Carpenter: Methods of Measuring Respiratory Exchange in Man, Car- 
negie Institute Pub., 1915, No. 216. 

Porter: Nervous Mechanism of Respiration, Jour. Phys., 1894, 17, 455. 

Krogh: Mechanism of Diffusion through Lungs, Jour, Phys., 1915, 49, 

Burrows: Oxygen Pressure Necessary for Tissue Activity, Am. Jour. 
Phys., 1917, 43, 13. 

Synder: Respiratory Change in Heart Rate, Am. Jour. Phys., 1915, 27, 



Within narrow limits the temperature of the body is a 
variable condition. The average temperature is 36.8° C. 
(98.3° F.) as recorded in the mouth, 36.9° C. (98.4° F.) in 
the axilla, and 37.2° C. (98.9° F.) in the rectum; but these 
temperatures normally show an advance of about 1° C. during 
the day, with a corresponding recession during the night. 
The temperature of some of the internal organs is as much as 
2° C. higher than the axillary temperature, especially during 
the state of maximal functional activity. Also the tempera- 
ture may be slightly increased by active exercise, or by the 
the ingestion of much hot food, or of food readily oxidizable. 

Heat Production in the Body.— The principle source of heat 
is that evolved by oxidations, the combination of oxygen 
with certain freely oxidizable substances. The most effective 
individual producers of heat in the body are the glands and 
glandular structures, but the greater part of the body's 
heat is produced in the muscles. It will be recalled that at 
every contraction of a muscle, much dextroid material is 
oxidized to carbon dioxide and water; this conversion, though 
obscure in nature, is attended by the production of heat, 
just as oxidation of any substance outside of the body is 
attended by the liberation of heat; every muscle contraction, 
therefore, means the production of heat. Moreover, every 
utilization by the cells of food material, if oxidation be an 
element of the process, will manifest coincidentally the phe- 
nomenon of heat production. Some of the metabolic changes, 
particularly those involving hydrolytic cleavages, and those 
involving synthetic results, are not productive of heat, they 
may, in fact, absorb heat as a factor of the process. Nor 


does there appear to be much heat produced by the nervous 
system, even though a continuous supply of oxygen is so 
essential to nervous activity. 

The Loss of Heat from the Body.— With a constant produc- 
tion of heat in the body, it is essential that an equable bal- 
ance be maintained by heat loss, lest accumulation of heat 
prove prejudicial to physiological efficiency. It is apparent 
that the heat loss is a continuous though variable process, 
taking place through many avenues. The greatest amount 
of heat is lost from the skin through radiation and conduction; 
Vierodt estimates that 73 per cent of the total heat loss takes 
place by this means. About 14 per cent is absorbed as latent 
heat in the evaporation of moisture from the surface of the 
skin; about 7 per cent is lost in vaporization of water from 
the respiratory surfaces; about 3.5 per cent is absorbed in 
warming the inspired air, and about 2 per cent is lost in the 

However these estimates do not represent constant rela- 
tive values. Naturally with decreases in outside tempera- 
tures a greater amount of heat will be expended by the body 
in warming the inspired air; and an increased amount will be' 
lost from the skin by radiation unless adequate protection 
be provided for the surface of the body. With high tempera- 
tures and low relative humidity, heat loss by vaporization 
from both the skin and respiratory passages increases rapidly; 
but if the relative humidity runs high, surface vaporization 
is markedly interfered with. The combination of high tem- 
perature and excessive humidity is one to which the body 
has most difficulty in obtaining adequate adjustment, inas- 
much as both radiation and vaporization are unduly 

Regulation of Heat Production.— Heat production is regu- 
lated in part by the amount of food material oxidized, and 
in part by the oxidation taking place through muscle activity. 
The oxidation of fats and sugars is accompanied by the 
production of considerable heat; and in cold weather and in 
cold climates this source of heat is augmented by the increased 
ingestion of these varieties of food material. 

Heat production varies inversely with the temperature of 



the air, maintaining the optimum balance so long as the 
regulating mechanism is mtact. Some experiments made 
on a guinea-pig showed that heat production as measured 
by carbon dioxide elimination diminished 50 per cent in a 
change of temperature from to 30° C. 

A more important means of regulating heat production is 
through muscular activity. It is a common experience when 
one feels chilly he can readily regain a feeling of comfortable 
warmth by means of vigorous exercise. If he does not take 
the exercise, not infrequently there is a reflex stimulation 
through the motor centers, and involuntary muscle activity 
in the form of shivering takes place, thereby producing 
enough heat temporarily to tide the body over its present 
depression and need. The relation of exercise to heat pro- 
duction is well shown in the following table adapted from 
Starling : 

Heat eliminated: 

Radiation In urine In water 

and and vaporiza- Total in CO2 Protein 

conduction feces. tion. calories. excreted. consumed. 

At rest . 1850 c. 26 c. 521c. 2397 230.4 G. 98.8 G. 

At work . 3802 c. 29 c. 743 c. 4574 705.0 G. 109.4 G. 

Physiological Oxidations.— Concerning the mechanism of 
the process of oxidation very little is definitely known. The 
following tentative hypothesis is as widely accepted, perhaps, 
as any other. The oxygen does not pass directly from the 
hemoglobin of the blood to the substance to be oxidized, 
but seems to undergo some intermediate transformation, 
whereby it becomes loosely united with a middleman sub- 
stance to form an oxidase or a peroxidase, bodies analogous 
to hydrogen peroxide in their promptness and power of 
transferring oxygen. These substances stand ever ready on 
the threshold of circumstance to serve as oxidizing agents, 
whether to render innocuous waste material from the cell, 
or to add energy to a cell's dynamic manifestations, or to add 
to or accelerate protoplasmic integrations. The oxidase or 
peroxidase seems surcharged with oxygen ions which are 
readily and rapidly released in the presence of an oxidizable 
substance of lower potential or of negative charge. 


Regulation of Heat Loss.— Since the greater part of bodily 
heat is dissipated from the surface of the body, the mechanism 
for regulating this loss must be associated with the skin area. 
Such a mechanism is found in certain reflexes which influence 
the caliber of the cutaneous bloodvessels, and some associated 
reflexes which affect the activity of the sweat glands. Thus 
lowering of the atmospheric temperature so acts upon certain 
of the sensory nerves as to induce a vasoconstriction through- 
out the exposed area. Elevations of the temperature has a 
reverse effect; thus when temperatures are high, the cutaneous 
bloodvessels dilate, more warm blood circulates near the 
surface of the body, and there is a resulting acceleration of 
heat conduction and radiation. When the external tempera- 
ture falls, contraction of the arterioles and capillaries lessens 
superficial circulation, and thereby diminishes the possibility 
of extensive heat loss by this means. 

The sweat glands are similarly affected. Elevations of 
external temperature bring on an increased activity of the 
sweat glands, more water than usual is poured out onto the 
skin, and its vaporization from the surface of the skin con- 
sumes heat at the rate of 0.5 calorie for each gram of water 

Analogous reflexes are excited by overproduction of heat 
within the body such, for instance, as accompanies muscle 
activity. In this case the initiation of the reflex is chemical, 
presumably, the effect on the vasomotor and sweat centers 
of various substances in the blood, and perhaps of the ele- 
vated temperature of the blood itself; this centric irritation 
produces a dilatation of the cutaneous bloodvessels and 
heightens the activity of the sweat glands, with a correspond- 
ing increased dissipation of the body heat. 

Another avenue for the dissipation of heat is the respira- 
tory tract, though this means is of less importance to man 
than to some of the lower animals, particularly the canines. 
But the increased rapidity of respiration, accompanying 
vigorous muscle activity, inevitably requires a greater number 
of heat units for warming the inspired air and for vaporizing 
the moisture which saturates expired air. All have probably 
noticed how birds and dogs pant on hot days; thus these 



animals find in respiratory heat dissipation some compensa- 
tion for radiation deficiencies at the surface of the body. 

The bodies of most animals living in cool or cold climates 
are more or less protected from excessive heat loss by means 
of their hairy coat. This covering having been largely lost 
by man in the course of his evolution, it becomes necessary 
that artificial covering be substituted. So one wears clothing 
which, by means of the still air enmeshed in the interstices, 
serves to greatly impede and diminish heat convection from 
the body. Heat radiation continues with little or no abate- 
ment, but convection of this heat takes place much less 
rapidly through layers of clothing than it w^ould if the body 
was exposed to currents of air. The relative efficiency of 
various kinds of clothing depends on the completeness with 
which the fabric retains dead air in its meshes. More still 
air seems to remain meshed in the tangled curls of woolen 
clothing than in any other kind of fabric; hence, woolen 
clothing is the warmest. 

All may have noticed how some animals increase the effi- 
ciency of their furry covering in cold weather by elevating 
the hair, thereby deepening the area of insulation. An 
atavistic attempt at a similar effect is seen in the common 
phenomenon known as "goose flesh;" in this picture the 
chilling of the surface produces a reflex contraction of the 
eredores pilorum muscles thereby elevating, even though 
abortively, the scanty hair covering of the body. 

The Nervous Control of the Heat Mechanism.— In previous 
paragraphs it has been noted how stimulation of sensory 
areas by heat or cold, or the chemical effects or muscle activ- 
ity, induces a reflex through the vasomotor center. A similar 
effect has been noted of local influences upon sweat glands 
and hair muscles. Any other heat-regulating mechanism 
than these adjustment coordinations of important service 
reflexes has not been demonstrated. Experimental evidence 
indicates that artificial lesions of various parts of the nervous 
system are accompanied by disturbances of the normal heat 
regulation of the body. For example, injury to the striate 
body increases both heat production and heat loss; also injury 
to the pons Varolii increases heat production, but has little 


effect on heat loss. Experimental lesions in the optic thal- 
amus, the septum lucidum, and the medulla, also disturb 
the heat regulating mechanism. Hemorrhages in the region 
of the striate body are accompanied by great increases in 
heat production. In fact, both laboratory and clinical evi- 
dence seem to indicate that any acute irritation of the central 
nervous system will produce disturbances of heat production 
and loss, but in just what manner is unknown. No definite 
heat center has been ascertained; from present evidence, 
perhaps, it would seem none is essential. 

The degree of external temperature endurable by man 
depends considerably on the relative humidity. The opti- 
mum temperature would seem to be about 68° F., with a 
relative humidity between 50 and 70. But for a short time 
a man can stand a temperature of 200° F. provided the air 
be exceedingly dry; yet he can hardly endure a temperature 
of 90° F. when the relative humidity is about 95. The 
extreme cold a man can endure will depend largely on the 
constancy and rapidity of heat production, and the measures 
taken to prevent heat dissipation. When unprotected by 
suitable clothing the body may readily succumb to tempera- 
tures comparatively not very low. 


The skin has several important functions to perform. 
These are: Protection; sensations of touch, pressure, heat, 
and cold; regulation of the body temperature; excretion. 
The part played by the skin in assisting in the regulation 
of body temperature has been considered in the preceding 
chapter; its dependence on the temperature variations will 
be considered soon. 

Of leading importance is the service the skin performs in 
protecting the body from invasion by foreign organisms. It 
is able to do this by means of its tough, horny epidermis 
through which the majority of bacteria are able to make 
their way with difficulty or not at all. But if a lesion of 
the skin occur, bacteria will find therein a favorable site for 
rapid development; it thus becomes very important that this 
protective function be maintained at the highest point of 

The horny layer is kept in a condition of flexibility by 
the continuous secretion through the hair follicles of a fatty 
wax-like substance termed sebum, which also protects the 
skin from maceration. The sebum probably contains minute 
amounts of waste matter. 


The function of heat dissipation is closely associated with 
the activity of the sweat glands. These glands seem to be 
in a constantly active state, producing what is generally 
termed "insensible perspiration;" this amounts to approxi- 
mately 500 cc. a day. However, whenever there is any undue 
increase of either internal or external temperature, the 


activity of the sweat glands becomes markedly increased; 
and the resulting vaporization of the sweat involves the 
absorption of many units of heat. The accelerated secretion 
of sweat under these circumstances seems to be a nervous 
reflex, which may be internal or external in its inception 
as there appears to be definite secretory fibers to the sweat 
glands. The most common exciter of the sweat glands con- 
sists in elevations of the atmospheric temperature, and in 
chemico-thermal excitants from active muscle; but the glands 
may be excited to unwonted activity by dyspnea and strong 
emotions, as well as by some drugs. 

The average secretion of sweat amounts to about 2 liters 
every twenty-four hours. The perspiration contains over 
98 per cent water, about 0.5 per cent sodium chloride, and 
mere traces of the several organic constituents found in 
blood plasma. Under normal conditions these organic 
substances are too minute to be looked on as excretory 
products; it would seem that their presence is more probably 
adventitious; therefore, the secretion may be considered 
simply as a means for maintaining both temperature and 
water equilibrium. However there is a constant though 
slight exhalation from the skin of carbon dioxide; this 
increases considerably with any increased activity of the 
sweat glands; some of this may be truly respiratory from the 
body tissues, similar to that which normally takes place in 
the frog, but a larger part is more probably a distinct waste 
product arising from katabolic changes taking place within 
the glands. 

The sensory activity of the skin is also of great impor- 
tance. This activity is manifested as the sense of touch, the 
sense of pain (the sense of pressure), and the temperature 
sense for making discriminations between hot and cold. 


The sense of touch shows two qualities, perception of 
contact with cutaneous surfaces, and discrimination as to 
the spatial relationships of two or more contacts. Touch 
proper is mediated by touch corpuscles in hairless regions, 


and by the circumfollicular groupings of nerve terminals in 
those regions supplied by hair, the hair itself serving as an 
accentuating lever for transmitting the pressures of delicate 
contacts. These latter areas are sharply localized, and while 
they are exquisitely sensitive to light pressure contacts, 
they seem devoid of a sense of pain. The acuteness of the 
sense of touch varies in different regions, being most delicate 
on the tip of the tongue, the nose and the lips; next on the 
fingers, forehead, palms and thighs; least delicate on extensor 
surfaces, the back, and the loins. 

Discrimination of spatial differences also varies with the 
location. The most sensitive discriminative area is the tip 
of the tongue, followed by the tip of the fingers, palmar 
surface. The area of poorest discriminative capacity is the 
middle of the neck or back. Various experiments, and some 
clinical observations, indicate that the sense of discrimina- 
tion is mediated by a different set of nerve fibers from those 
supplying simple tactile sensibility, inasmuch as in some 
lesions of the spinal cord the latter sensibility for a given 
skin area may be lost while the former sensibility is retained. 
It is stated that the discrimination fibers pass uncrossed 
up the posterior funiculi of the cord while the simple tactile 
fibers ascend, hetero-laterally, through the antero-lateral 

It is customary to include among the cutaneous functions 
that of the pressure sense, but the nerves mediating the sense 
of pressure and the sense of resistance are associated not 
with the skin but with the muscles or with the expansions 
of the tendons into the muscles. As a consequence, a pres- 
sure not of a painful nature is mediated by the tactile sense 
as a touch solely, but the tension placed thereby on muscle 
gives a reaction in consciousness different in modality from 
that of mere tactility. This muscle sensibility has, of course, 
a much wider function than that of mere mediation of external 
force; it is the great means whereby the higher centers of 
coordination and equilibration, as well as consciousness itself, 
receive essential awareness of the state of tonicity of muscle 
or of the state of contraction then existent in any muscle, 
or set of muscles. The pressure sensations indicative of 


external force are well localized by the sensorium, probably 
because of the associated tactile sensations. The other 
sensations coming from the muscles, as well as those related 
ones from the joints and ligaments, have but a dim definite- 
ness in consciousness, though in most cases they adequately 
apprise consciousness of variations in muscle tonicity. 
Moreover, multitudinous repetitions so train the apprehen- 
sive area as to therein develop a keen discrimination, and a 
purposive utilization, of the intricate variations of muscle 


Besides the sensory points on the skin mediating touch 
and temperature, there are other spots relatively insensitive 
to low grades of stimuli but manifesting highly disagreeable 
sensations when the intensity of the stimulus increases to 
the critical point. There are some areas, like the cornea, in 
which the minimal stimulus perceptible proves likewise a 
painful one. On the other hand, in some pathological states, 
a given skin area may become analgesic without being anes- 
thetic. This indicates there are definite sensory points 
mediating pain, and that the pain sensations are transmitted 
by special nerves. The following confirmatory evidence 
from the work of von Frey may be cited: Repeated electric 
stimuli, of a speed as low as five a second, applied to a pain 
spot give a continuous sensation; whereas electric stimuli 
as high as 130 shocks a second applied to a touch spot give 
a discontinuous sensation that is not necessarily of a painful 

Sensations of pain are not confined to the skin, but seem 
to arise from any area having afferent nerve fibers. Periph- 
eral pain is localized very accurately unless sensory anes- 
thesia be present; but painful sensations from any internal 
organ will usually be inaccurately localized, especially if the 
sensory fibers coming from this area of low sensibility be 
segmentally associated in the cord with afferent fibers from 
a surface area of relatively high sensibility; in such a case, 
misreference is made to the skin area. For example, inflam- 


mation of the pleura at the costo-diaphragmatic reflection 
will not infrequently give needle-like sensations in the skin 
over the acromial region of the shoulder. 


It is readily demonstrable that the small subdivisions of 
any cuticular area are not equally responsive to variations 
in temperature. By means of a stylus kept at a constant 
temperature of 40° C, one may map out on his skin a punc- 
tate area showing spots responsive to the heat stimulus of 
the hot stylus, with intermediate areas giving no heat 
response. If the same area be now charted with a stylus 
cooled to 25° C, a series of spots responsive to cold will be 
found; these cold spots will not be identical with the hot 
spots, as application of ordinary heat to the cold spots does 
not give a sensation of warmth, nor does the application of 
cold to a warm spot give the sensation of cold. Each spot 
seems to possess a specific reaction to certain rates of vibra- 
tion, the dividing line in any case being the present tempera- 
ture of the surface of the body. The sensibility of the 
temperature sense seems to vary w4th location, being most 
sensitive on the nipples, chest, nose, flexor surfaces of the 
forearm, and abdomen; the sense varies also with the present 
condition of the skin, especially as related to any immediately 
previous stimulation of these sense organs. At the ordinary 
temperature of the skin, sensitive subjects can appreciate 
a difference as small as 0.2° C, but this sensibility diminishes 
with either a rise or fall in the skin's temperature; in almost 
any case the sense of cold is more promptly responsive than 
is the sense of heat; this may be due somewhat to the fact 
that the cold spots are more widely distributed. A peculiar 
phenomenon sometimes elicited, is the specific stimulation 
of a cold spot by the application of a stylus heated to above 
45° C. 

The temperature sense serves to make the organism aware 
of the thermic condition of its environment, with the possi- 
bility of a corresponding adaptation thereto. 

In summarizing the several functions of the skin and the 


sensations connected with cutaneous sensibilities, use may 
be made of the classification suggested by Head and Rivers. 
This classification divides the sensations into the epicritic 
and protopathic. The epicritic sensations are those which 
are very accurately localized, and which manifest fine dis- 
criminations. The protopathic sensations are those which 
refer to sensations of a grosser quality, and those which tend 
to apprise consciousness of conditions which might readily 
prove dangerous to the organism as a whole. Then there 
are other sensations which mediate either pressure on the 
skin or indicate the degree of muscle tension. 

f Heat and cold discriminations in small differ- 
Epicritic sensibil- j ences between 26° and 37° C. 
ity I Tactile sense. 

1 Tactile discrimination. 
Protopathic sen- ^^^^^^neous pain. _ 

., .|^, j Heat discrimination over 38° C. 

^ I Cold sensations under 25 ° C. 

I Pressure. 
Subcutaneous or I Deep pain. 

deep sensibility | Muscle or ligament tension. 
[ Joints relationship. 



The several functions of the body could not be utilized 
at all were not the organism equipped with some means of 
assimilating sensory impressions and appropriately respond- 
ing thereto. Such a mechanism involves at least three 
factors: (a) A peripheral area sensitive to external impres- 



/'■■■^*^^_^--^' /9 


V'Bf AH;rN>A 

"^m w^% 



Fig. 32. — Amoeba moving. 

Fig. 33. — Amoeba quiet. 

sions; (6) a medium or means for transferring the ensuing 
force evoked ; and (c) a motile apparatus capable of effecting 
changes of the spatial relationships of the whole organisms 
or of some of its parts. All of these factors are present to 
some degree in all organisms, at some period or other of 
their existence even though in some cases the motile elements 
appear recedent (Figs. 32, 33, 34, 35). 

In the lowest forms the several factors are not individually 
discernible, but their essential presence is experimentally 



deducible. In higher forms the several parts are differentiated 
into definite systems; that is, there are: (a) a sensory area of 
intricate and extensive responsiveness; (6) a conductive 
system having two essential elements, to wit, nerve fibers 
serving as means of transmittal and intercommunication, 
and intermediate nerve cells which are integrative; and (c) 
a contractile system which alters its diameters in response 
to the various stimuli, pure or integrated, coming from the 
sensory area (Fig. 36). 

Fig. 34. — Flagellatum active. 

Fig. 35. — Flagellatum quiet. 

In protozoa no such systemic differentiation is discover- 
able, though the readily observed sequence of phenomena 
indicates the presence of sensory receptiveness and adaptive 
response. With amoeba, for example, the presence of food 
material induces the reaction of autrusion and envelopment, 
but the stimulus of a weak electric current induces the 
reaction of resistance (Figs. 32 and 33). These changes of 
spatial relationships are effected by some intrinsic means not 
yet deciphered, but a means which may safely be considered 
the anatomical anlage, as well as the physiological proto- 
type, of the sensory-neuro-muscular apparatus of the higher 
forms (Fig. 37). 



Several varieties of motion are present in the lower forms 
of life, such as the protoplasmic flowing of the Amcebidce, 
the active propulsion of the Flagellata (see Figs. 34 and 35) 
and InfnsoricB, as well as the starting contractility of the 
stalk of the Vorticellidce (see Fig. 36); yet neuro-muscular 

Vorticella seeking food. 


Vorticella drawing away from a 

Fig. 36 


tissue of definitive type is first observable, as a relatively 
differentiated form, in some of the Ccelenterata (Hydra, for 
example). In this most primitive of discovered types there 
is present the single layer of ectodermal cells which transmit 
surface impressions through the intracellular protoplasm to 
a subdermal differentiated process of the same cell, and this 



process responds to the stimulus by contracting. Here 
there is a specialization of function within different parts of 
the same cell— an outer sensory part that receives the impres- 
sion and an inner motile part that manifests a reaction of con- 
tractility. In a slightly higher form (Cnidaria), the contrac- 
tile portion becomes elongated so as to form a protoplasmic 
process extending mesially. In a yet higher form of the same 

Fig. 37. 

-Tentacle of Eucopella, showing development of ganglion cells 
(After Parker and Haswell.) 

type (Cnidaria) the contractile element has the appearance 
of a long fiber lying under the epithelium to which it is 
joined by a thin layer of protoplasm. Some of the sensory 
cells develop delicate immobile hairs projecting outward, 
and apparently some of the adjacent sensory cells become 
enfolded and submerged yet retain their connections with 
both the surface sensory cells and with the subepithelial 



contractile elements; such submerged cells apparently func- 
tion as intermediate or ganglion cells (see Fig. 38). Grad- 
ually these ganglion cells become more deeply submerged, 
with a consequent lengthening of the communicating fibers. 
Yet later, evolutionally, there is a grouping of the principal 
ganglion cells in a longitudinal chain or chains, with a greater 
or less development of those groups of cells lying near the 
anterior end of the animal. At the same time there goes on 
an increasing specialization of the sensory cells to a selective 
response to various forms of excitation; also there develops 


Fig. 38. — Diagram to illustrate evolution of neuro-muscular development 
from epithelial cells. 

a systematic grouping of the contractile elements to definite 
ends, some manifesting regular rhythmic movements, some 
showing intermittent rhythmic activity, and some being 
but reflexly responsive. This developmental sequence is 
illustrated in outline in Fig. 38. 

In this conception the nerve fiber is looked upon as a con- 
ductor merely for the transference of neural energy from one 
point to another. The nerve cell, however, is considered to 
have a dynamic function for the augmentation, or trans- 
mutation of neural energy. The raw material for its kinetics 





//^ ^^,p 



I Reptilia 


Fig. 39. — Diagrammatic view of the brain in different classes of verte- 
brates. CB, cerebellum; PT, pituitary body; PN, pineal body; C.STR, 
corpus striatum; GHR, right ganglion habenulse; /, olfactory; II, optic 
nerves. (Gaskell.) 



is derived, of course, from tjhe general food supply of the 
blood; its special adaptability consists of its power to convert 
this static force into the specific energy peculiar to neural 

Passing over the many interesting points in the develop- 
mental history of the nervous system, the main features of 


Motor root 
Sensory root 

Ganglia of VII. and 
VIII. Ns. 

Auditory vesicle 

Fig. 40. 

-Exterior of brain of human embryo of four and a half weeks. 
(Fromi model by His.) 

which are reviewed in Embryology, consideration may be 
given to the system in Vertebrates as simplifying a study of 
the physiology of the human brain. In Amphioxus there is a 
dorsal nerve tube extending the whole length of the body; 
this tube expands anteriorly into a simple bilateral vesicle. 
In the Chordates, this anterior expansion becomes sub- 


divided into three vesicles, the prosencephalon or fore-brain 
mesencephalon or inid-hrain, and metencephalon or hind- 
brain.(Figs. 39 and 40). Further ascent in the animal scale 
is accompanied by increasing differentiation and complexity 
of this anterior portion, until the intricate differentiation 
found in man is wrought; yet each of the more mature por- 
tions can be traced developmentally from the three primitive 

The floor of the prosencephalon, or fore-brain, becomes 
greatly thickened laterally, forming two large masses of 
gray matter termed the corpora striata; these constitute the 
chief part of the fore-brain in the lower vertebrates. From the 
infero-lateral aspect of the prosencephalon anteriorly, early 
bud out protuberances which bend forward and become the 
anlages of the optic stalks (Fig. 40). Extending out ante- 
riorly from the inferior border of the prosencephalon are 
two slender lobes of the brain; these become the olfactory 
lobes, although called the rhinencephalon at this early stage. 
Between the floor of the fore-brain and its immediate roof 
is a narrow chink-like space, the third ventricle; it is con- 
nected antero-laterally with the first and second ventricles 
through two small apertures, the foramina of Munro; postero- 
mesially it communicates with the fourth ventricle in the 
metencephalon by a small passage in the mid-brain termed 
the aqueduct of Sylvius. The prosencephalon expands 
greatly in every direction supero-laterally, covering and 
concealing the other parts of the brain (see Fig. 43); its 
superior surface becomes infolded in sulci and furrows, the 
extent and complexity of which indicate the phylogenetic 
position of the animal; this tremendous expansion greatly 
extends the available area for sensory registration and motor 
direction. The two lateral vesicles are connected by a great 
mass of intercommunicating fibers termed the corpus callosum; 
by means of this great bridge the two sides of the brain are 
brought into a coordinating harmony of activity. 

In the higher vertebrates the diencephalon develops two 
large ganglionic masses, called the thalami (Figs. 40, 41, 42 
and 43) ; these serve as important relay stations for afferent 
impulses. Superiorly there is a curious structure, the pineal 



gland; this is probably a vestigial organ of light sensation. 
Inferiorly there is a downward growth termed the hypophysis 
cerebri (Figs. 41, 42 and 43) ; this is a ductless organ the secre- 
tion of which has an important influence on the development 
of bone. Postero-superiorly, in the mesencephalon, is a 
small bilobed structure which in the lower forms is termed 

Ganglion habenulce 

Hypophysis cerebri 

Fig. 41. 

-Exterior of brain of human embryo of five weeks, 
by His.) 

(From model 


the optic lobe as it serves as an important optic center 
the higher forms it is quadrilobed and is termed the corpora 
quadrigemina, and serves as relay and coordinating stations 
for auditory and ocular impulses (see Figs. 40, 41 and 43). 
Laterally and postero-inferiorly are developed two heavy 
strands, the peduncles, connecting the optic thalami with the 
medulla and serving to transmit impulses from the lower 



centers of the brain stem to the higher, and also connecting 
the motor areas of the cerebrum with the spinal cord. 

Arising from the lateral portions of the roof of the fore- 
part of the metencephalon is a mass of nerve tissue termed 
the cerebellum; this is especially well developed in the higher 

Choroidal fissure 

Recessus infundihuli 

Fig. 42. — Median sagittal section of brain of human embryo of three months. 
(From model by His.) 

forms; it is the great central organ of coordination and equili- 
bration (see Figs. 43 and 59) . Anteriorly two heavy masses 
of -nerve j&bers pass forward to convey impulses between the 
cerebellum and the cerebrum; these are augmented by a 
second median mass, which passes anteriorly and ventrally 
to the main stem to form the structure known as the yons 



Varolii; posteriorly, are two more heavy strands forming 
the chief connection between the cerebellum and the spinal 
tracts. The remaining portion of the metencephalon, 
expanded anteriorly and ventral ly in connection with the 
mesencephalon, and continuous posteriorly with the spinal 
cord, is termed the medulla (see Fig. 43) ; in this portion of the 
brain stem are located the great nerve centers controlling 
the vital activities of the body. 

Gyms dentatus 
TcBTiia thalami 


Choroidal fiss 

Post, commissure 

Corpora quadrigemina 
Cerebral aqueduct 
Cerebral peduncle 


IV. ventricle 

Corpus callosum 
Septum pellucidum 
Anterior commissure 

Lamina terminalis 

Optic chiasmrt 

III. ventricle 


/X Medulla oblongata- 

Fig. 43. 

-Median sagittal section of brain of human embryo of four months. 


The spinal cord is a tubular structure passing caudad 
from the cephalic region. It is composed of masses of com- 
municating and transmittal white fibers forming the wall 
of the cord, and of continuous areas of gray ganglionic 
cellular structures in the inner portion. The cord gives 
origin to a regular series of nerve trunks from both its ante- 
rior and posterior aspects; the anterior or ventral trunks are 


efferent and motor; while the posterior are afferent, and 
sensory in function. Certain fibers from both the anterior 
and posterior trunks unite and pass to the front of the verte- 
bral column, and there establish two longitudinal ganglionic 
chains forming the major portion of the Autonomic System; 
this has extensive distribution to all the internal organs of 
the body the activity of which is subject to the influences 
coming in from both the autonomic and the central nervous 

Functions of the Spinal Cord.— Among the higher vertebrates 
possessing a segmentation arrangement, the Annelidce for 
example, the reactions of each segment are presided over by 
a ganglion or ganglia located within that segment; influences 
from neighboring or distant segments are minimal, except 
those coming from the projicient area at the cephalic extrem- 
ity; these impulses from the head end may have either 
inhibitory or acceleratory effects on all the segments, but 
the dominant influence over the general activities of a given 
segment resides in the ganglia of that segment. Higher up 
in the animal scale, the chains of ganglia controlling definite 
areas are seen to become more and more closely conjoined, 
and though each segmental area still retains its ganglionic 
association for the vegetative activities, yet the major con- 
trol over the several areas, especially such control as involves 
coordination of all the activities for the welfare of the whole, 
becomes gradually transferred more and more toward the 
continually enlarging cephalic group of ganglia. At the same 
time the primitive arrangement in segments gradually 
becomes altered, so that in the higher vertebrates little of 
this primitive arrangement persists in the adult form, though 
readily discoverable in the embryo type. The original func- 
tion of reflex action continues in the cord, but increasingly 
the substance of the cord becomes occupied with a greater 
relative percentage of fibers of communication and trans- 

The ganglionic cells serving as reflex centers, or as relay 
stations, are located deep in the substance of the cord (see 
Fig. 44), constituting its gray matter. The fibers of com- 
munication surround the gray matter and occupy, therefore, 



the surface area. The fibers of transmittal have regular 
entrances and exits from the cord, in almost the primitive 
segmental fashion dorsally, but less so ventrally. Section 
experiments have shown that the dorsal root fibers in the 
higher vertebrates are probably all afferent and sensory, 
while the ventral root fibers are all efferent and motor. 
Therefore, sensory impulses from all over the body (excepting 

Posterior median sulcus 

I Pn.iterinr nm.pci^d'n. -ipptum 

nerve roots 

ostero-lateral sulcus 


Format io 


Anterior nerve roots Anterior median fissure 

Fig. 44. — Transverse section of the spinal cord in the mid-thoracic region. 


those areas supplied by the cranial nerves), impulses con- 
veying impressions of touch, pain, heat, and cold, muscle 
tensions and joint relations, all pass in through the fibers 
of the posterior roots. The most primitive of these fibers, 
apparently retaining their primitive functions, enter the 
cord to pass directly to the anterior horns of the same side 
(and in small measure to the anterior horns of the opposite 
side) where they complete important reflex arcs by arboriz- 



ing around the dendrites of the motor cells. (See 1 m Fig. 
45) . Among the next older fibers are those passing to neigh- 
boring areas of the cord, there to link up with other sensory 
fibers, or to pass to motor cells of a near-by segment (see 2 

Fig. 45. — The four types of reflexes. 

in Fig. 45). Other ancient fibers are those passing to the 
column of Clark where they terminate by arborizing around 
the dendrites of new cells whose axons pass lateral to the 
surface of the cord to ascend in the direct cerebellar tra^ct of 


the same or opposite side to the ''superior worm" of the 
cerebellum (see 3 in Fig. 45). The larger proportion of the 
sensory fibers ascend in the columns of Goll and Burdach to 
terminate respectively in the gracile and cuneate nuclei, 
whence the impulses are relayed to higher centers of recep- 
tion in both the cerebrum and cerebellum (see 4 in Fig. 45). 
Other sensory fibers pass into the tract of Lissauer where 
they soon divide into ascending and descending branches 
and terminate around the cells of the substantia gelatinosa 
in some of the adjacent segments, mostly on the same side 
but with a few collaterals to homologous structures in the 
opposite side of the same segment. 

This extensive distribution of the afferent fibers serves 
an important physiological utility. The most primitive use, 
that of a reflex switching of sensory impressions into motor 
responses, is fundamental. A second utility is the impressing 
of adjacent areas so that a coordinating action may be ini- 
tiated from several segments of the cord, a matter of much 
importance for securing a correlated activity of those limb 
muscles receiving motor impulses from several adjacent 
spinal segments. This segmental coordination is further 
augmented by a large series of internuncial fibers extending 
from one segment to another up and down the cord in the 
antero-lateral field. A third utility is the transmission of 
sensory impulses to the cerebellum for coordinating integra- 
tions. A fourth utility is the transmission of sensory impulses 
to the cerebrum, to the end that consciousness shall be 
apprised of the organism's condition and environment. From 
these utilities it follows that sensory impressions may result 
in simple reflex motor response only; or in complex motor 
response with extensive integrated and adaptive coordina- 
tion from the cerebellum; or in a complex motor response 
having any of the preceding features, but more or less modi- 
fied by the reactions produced in consciousness as expressed 
by the multifarious impulses proceeding from the cerebral 
motor area. 

The cerebrum exerts its modifying influence by means of 
the great number of efferent fibers streaming down from the 


pre-Rolandic area, through the direct and crossed pyramidal 
tracts of the spinal cord, thence to the ventral horns of gray 
matter there to arborize around the dendrites of motor cells 
whose axons are distributed to the musculature of the body. 
These modifying influences are not essential to the vegeta- 
tive existence of the animal, but add greatly in effecting 
needful adaptations to changes in environment. 

A very important item in the reflexes is that concerned 
with the afferent fibers from the muscles and tendons whereby 
constant impulses originating in variations of muscle tensions 
are reflected through the motor nerves to the muscles, thus 
keeping the muscles in a state of constant tonicity. 

This tonicity is inhibited in groups whenever a sensory 
impulse results in a group contraction of opposed muscles; 
that is, sensory impressions, eventuating in flexor activity, 
simultaneously produce an inhibition of the extensor muscles 
attached to the same limb segment. 

Entering the spinal cord is a continuous stream of impulses 
from all over the body, each of which might conceivably 
be potent for inducing a reaction of some sort; yet when so 
many impulses are so rapidly pouring into the cord, only a 
few can be effective in securing a motor response; in such a 
case, the attaining of activity by any series results in a sup- 
pression of such adjacent impressions as at that moment are 
not cooperative. Not infrequently, however, a submerged 
reflex will be exprest when the earlier dominant reflex has 
expended its force. Almost invariably, that stimulus which 
in nature is protopathic will secure domination. 

Afferent nerves from muscles are indispensable to the 
effective use of muscle, inasmuch as, through the impressions 
they convey, the reflex centers in the cord, cerebellum, or 
sensorium are apprised of the relative position and tension 
of the muscles involved. It is just as important that the 
activity of a muscle be accurately controlled or exactly 
checked as that it be initiated ; and the afferent fibers furnish 
the requisite information. In certain diseases, like tabes 


dorsalis, where afferent muscle sensations are cut off by the 
degeneration of the posterior spinal tracts, the patient 
loses the power to control his voluntary efforts, the muscles 
responding spasmodically and in an exaggerated and inco- 
ordinated manner. Whenever there is permanent interference 
with these nerves, such that their normal impulses to the mus- 
cles are lacking, the muscle tonicity soon disappears. This 
interesting interrelation was formerly supposed to be due to 
a so-called trophic influence involving a special neural effect 
on the muscle's nutrition, but present evidence seems to 
indicate that the reaction is one depending chiefly on activi- 
ties rather than on assimilation. 

Another important factor in spinal reflexes is the impres- 
sions derived from the cutaneous area. When these impres- 
sions are entirely cut off from the fore limb, motor paralysis 
ensues even though the motor side of the reflex arc be intact 
throughout. But in the hind limb, the effect is not so com- 
plete; motor paralysis does not here ensue, but if the patient 
closes his eyes and keeps his feet near together he will be 
unable to maintain his equilibrium, owing in part to his 
deprivation of cutaneous sensibility in the soles of his feet. 

Conduction Functions of the Spinal Cord.— More and more 
in the progression upw^ard in the animal scale the primitive 
faculties of the cord become subordinated to the influence of 
the higher centers of the nervous system. This shifting of 
directive and coordinating control involves a corresponding 
increase in the number and arrangement of the fibers of 
communication, both to and from the higher centers. These 
afferent and efferent fibers are fairly well grouped in different 
areas of the cord making classification of them relatively 
easy. It must continually be borne in mind, however, that 
each of the fibers in its course gives off at frequent intervals 
many fine branching collaterals, thereby serving reflex con- 
nection and coordination over an extensive field. 

Assuming that all ascending tracts convey afferent impulses 
the following tentative classification may be made: Up the 
columns of Goll and Burdach (see Fig. 46 and explanation) 
pass impulses concerning cutaneous impressions having to 



Sensory root 

Motor root 

Fig, 46. — Diagram of the spinal cord showing a cross-section at about 
the level of the fifth cervical vertebra. Areas A to G inclusive, and tracts 
1 to 9 inclusive are concerned chiefly with impulses going to the brain ; areas 
H to L, and tracts 10 to 15 inclusive, are concerned chiefly with impulses 
going to muscle. 

Anatomical names of areas illustrated in Fig. 46: A, Postero-median fas- 
ciculus (column of Goll) ; B, postero-lateral fasciculus (column of Burdach) ; 
C, fasciculus spino-cerebelli (direct cerebellar tract) ; E, fasciculus antero- 
lateralis superf7cialis (Gower's tract); D, fasciculus spino-tectalis ; F, fascic- 
ulus spino-thalamicus lateralis; G, fasciculus spino-thalamicus ventralis; 
H, fasciculus cerebro-spinalis lateralis (crossed pyramidal) ; I, fasciculus 
rubro-spinalis; /, fasciculus tecto-spinalis ; K, fasciculus vestibulo-spinalis ; 
L, fasciculus cerebro-spinalis ventralis (direct pyramidal) ; M, fasciculus 
anterolateralis (antero-lateral ground bundle). 

Physiological avenues illustrated in Fig. 46: 1 and 2; impulses having 
to do with tactile discrimination, joint appositions, and muscle and tendon 
tensions, destined for conscious apprehension; 3 and 4 (homolateral), and 5 
and 8 (heterolateral), impulses having to do with cutaneous impressions, 
joint appositions, and muscle and tendon tensions, not destined for conscious 
apprehension but for cerebellar coordination and integration; 6, impulses 
concerned with sensations of pain; 7, impulses concerned with sensations 
of heat and cold; 9, impulses concerned with sensations of touch; 10, sub- 
volitional motor impulses of lower cerebral activities; 11, 13, volitional 
motor impulses of higher cerebral actiAdties; 12, impulses of vestibulo-motor 
equilibration adjustments; 14, impulses of oculo-motor position adjustments; 
15, sensory-motor reflexes; 16, impulses of segmental correlations. 


do with tactile discrimination, joint appositions and muscle 
and tendon tensions destined for conscious apprehensions 
(see A and B, and 1 and 2, Fig. 46). These are relayed in the 
gracile and cuneate nuclei, cross over in the mid-brain thence 
to the thalami whence they are relayed to the cortex. 

Similar impulses concerning cutaneous impressions, joint 
appositions, and muscle and tendon tensions not destined 
for conscious apprehension, but for the higher and more 
intricate forms of coordination afforded by the cerebellum, 
pass from Clarke's column to the direct cerebellar tract 
and to the tract of Gower (see C and D, and 3, 4, 5, and 8, 
Fig. 46), thence up the cord both homolaterally and hetero- 
laterally, to the cerebellum, terminating in the vicinity of 
the '^superior worm." Those traversing the direct cere- 
bellar tract enter the cerebellum by way of the inferior 
peduncle; those passing in Gower' s tract enter the cerebellum 
by way of the superior peduncle after traversing the medulla 
and pons. 

Impulses of touch and pressure (see 9 in Fig. 46) proceed 
up the posterior columns a few segments, then gradually 
cross over to the anterior columns of the opposite side (G in 
Fig. 46) and probably ascend to the thalamus, thence to be 
relayed to the cortex. Associated fibers in the spino-tectalis 
tract end in the vicinity of the corpora quadrigemina. 

Impulses concerning the sense of pain (6 in Fig. 46) pass 
at once from the posterior column over to the spino-thalamic 
fasciculus (E in Fig. 46) in the lateral column of the opposite 
side whence they proceed to the thalamus, there to be relayed 
to the cortex. Sensations of heat and cold (7 in Fig. 46) are 
transmitted along an adjacent path (F in Fig. 46). In addi- 
tion to all these there are myriads of short internuncial 
fibers connecting the several areas of different spinal seg- 
ments, both ventral and dorsal (M in Fig. 46), not only the 
adjacent ones but those of several segments distant. 

Concerning the descending tracts mention has already 
been made of the great pyramidal tracts, progressively more 
marked in the higher vertebrates, whereby the unconditioned 
reflex of the lower types becomes supplanted by controlled, 
educatable reaction. Motor impulses originating in the pre- 


Rolandic area — the great field of volitional control — are 
conveyed along the motor axons, down through the posterior 
limb of the internal capsule, through the cerebral peduncles 
to the medulla where about 90 per cent of the fibers cross 
to the opposite side, forming the crossed pyramidal tract 
{H in Fig. 46) ; this tract descends in the spinal cord, giving 
off numerous fine collaterals and terminals all of which end 
by arborizations around the dendrites of the motor cells in 
the anterior horns at different levels of the spinal cord (see 
H in Fig. 46). The remaining 10 per cent of the motor tract 
descends in the anterior pyramidal tract {L in Fig. 46) to 
terminate in a similar manner to the crossed fibers; the major- 
ity of the direct tract cross to the other anterior horn before 
terminating (13 in Fig. 46). Thus the motor division of the 
cord is directly connected with the volitional area of the 
cortex of the brain. 

Another descending tract of much significance is the rubro- 
spinal, or Monakow's bundle (/ in Fig. 46) . This is a fairly- 
well defined tract descending from the red nucleus in the 
tegmentum of the mesencephalon, through the medulla, 
and down the lateral column of the cord, just anterior to the 
crossed pyramidal tract, and terminating in the gray matter 
of the anterior horns. Because of the known connections of 
the red nucleus with the cerebellum, striate body and cortex, 
it is believed this bundle is an accessory motor tract, possibly 
one of non-conscious but higher coordinations, with special 
reference to the activity of the older motor ganglia in the 
brain (10 in Fig. 46). 

Lying anterior to the foregoing in the cord is another 
bundle (J in Fig. 46) having its origin in a group of cells in 
the pons in the same area where terminate the primary 
sensory fibers from the vestibular branch of the eighth nerve. 
The fibers of this vestibulo-spinal tract terminate in the 
gray matter of the anterior horns of the cord; it is therefore 
thought that this bundle is concerned with the reflex coordi- 
nation of muscle movements with the equilibrium impres- 
sions received from the semicircular canals in the internal 
ear (14 in Fig. 46). 

Evidence concerning the physiological significance of 


several other described tracts in the spinal cord, such as the 
olivo-spinal tract, and the reticulo-spinal tract is being slowly 
supplied by careful, laborious investigation. 


With progressive departure from the primitive type, there 
is corresponding increase in the complexity of the cephalic 
portion of the nervous system. More and more specializa- 
tion of function takes place, and important responsibilities 
are centered in limited areas. Many of these vital functions 
become localized in the medulla, a circumstance that is 
accompanied by marked anatomical variations from type. 

The columns of Goll and Burdach terminate in two heavy 
aggregations of gray matter termed the gracile and cuneate 
nuclei. These apparently serve as relay stations for sensory 
impulses. From these nuclei axons stream out in long ascend- 
ing arcs, crossing thus to the opposite side, whence, as the 
mesial fillet, they go on up to the thalamus. 

The central canal of the cord becomes widely expanded 
at the medulla, and loses its dorsal cover in the mid-region. 
(Fig. 47) . Here in the floor of the medulla, and in the deeper 
subjacent structures, are important groups of cells, lying in 
areas homologous to those occupied by the gray horns in the 
cord; these form nuclei of origin and reception for the fifth 
to twelfth cranial nerves. The anterior horns are displaced 
deeply dorsally by the heavy pyramidal tracts and by the 
olivary nuclei, and the posterior horns are displaced laterally; 
all the gray matter of the medulla is much reticulated by the 
great streaming of longitudinal and cross-white fibers. 

Continuing upward the gray matter of the posterior horn, 
but being steadily displaced laterally, is the nucleus called 
the fasciculus solitarius (see Figs. 47 and 48) which extends 
as high as the strioB acusticce; this is the nucleus of reception 
in the medulla for the sensory fibers of the seventh, ninth, and 
tenth nerves. The portion of the seventh which terminates 
here bears sensations of taste, and of common sensation, 
from the anterior two-thirds of the tongue; these fibers may 
probably be considered "an aberrant strand of the glosso- 




E. A. S. 

Fig. 47. — The cranial nerve nuclei schematically represented in a sup- 
posedly transparent brain stem, dorsal view. A, Motor nuclei; B, primary 
terminal nuclei of afferent (sensor) nerves. (Optic and olfactory centers 
are omitted.) (Gray.) 



pharyngeal;" their cells of termination occupy the upper 
reaches of the fasciculus, and also terminate in the dorsal 
sensory nucleus. The ninth, or glosso-pharyngeal, nerve 
(sensory division) conveys impressions of taste from the 
posterior third of the tongue, and impressions of ordinary 
sensations from the posterior third of the tongue, from the 
fauces, tonsils, Eustachian tube, pharynx and middle ear. 
The vagus, or tenth nerve, brings in sensory impressions 

Taste and common 
7 y sensation 

Anterior two-thirds of tongue 

Taste and common 

Posterior one-tiiird of tongue 

g , Sensation of contact 


Eustachian tube 
Middle ear 

^E IQ I Sensation of contact 

Dura mater 

External ear 




Bronchi-and subdivisions 





Fig. 48. — Scheme of functions of afferent branches, seventh, ninth, and 

tenth nerves. 

from the dura mater, external ear, pharynx, larynx, trachea, 
bronchi and their subdivisions, esophagus, stomach, and 
pericardium. The sensory continuations from this extensive 
field of reception are in part through secondary fibers which 
join the mesial fillet and so on to the higher centers, and in 
part through arcuate fibers passing to the cerebellum. 

More laterally in the floor of the fourth ventricle (see 
Fig. 47) and more superficially, lies the reception nucleus of 
the vestibular portion of the eighth nerve, concerned with 



impressions coming from the semi-circular canals. This 
nucleus is an irregular triangular area situated at the lateral 
angle of the fourth ventricle, extending upward into the 
pontine portion, downward into the closed area of the medulla 
and laterally ventral to the superior and middle peduncles. 

)e iters 

Roof nucleus 
of cerebellura 

^estibulo-spinal tract 


Fig. 49. 

-Diagram showing the connections between the semi-circular 
canals, cerebellum and cord. 

It is composed of two parts, a lateral portion termed Belters^ 
nucleus, and a dorsal or principal nucleus having a descend- 
ing part called the spinal nucleus, and an ascending part 
called the superior nucleus or the nucleus of Bechterew. 
Some uncertainty exists concerning the secondary paths 


from these several nuclei, but the following may be tenta- 
tively stated: The nucleus of Deiters (see Fig. 49) is a coordi- 
nating relay station receiving fibers from an important 
efferent tract from the opposite roof nucleus of the cerebellum, 
and fibers from the vestibular branch of the eighth nerve; 
the axons from these nuclear cells pass for the most part 
down the vestibulo-spinal tract of Monakow to end around 
the anterior horn cells as far down as the lumbar region. 
Deiters' nucleus serves therefore as an important internode 
connecting the equilibrating apparatus of the semi-circular 
canals, and the coordinating mechanism of the cerebellum, 
with the motor cells of the cord. From this nucleus some 
fibers pass also into the posterior longitudinal bundle to 
terminate around the nuclei of the fourth and sixth nerves, 
and possibly about the seventh, thus coordinating vestibular 
impressions with eye movements. Secondary paths from 
the principal nucleus are probably as follows : A large strand 
into the nucleo-cerebellar tract passes by way of the inferior 
cerebellar peduncle to the opposite roof nuclei of the cere- 
bellum; some fibers enter the arcuate strand passing to the 
mesial fillet of the same and the opposite side, and thence 
to the optic thalamus; commissural fibers connect the nuclei 
of Bechterew. Thus the fibers are related to cerebellar 
adjustment, besides giving consciousness apprisement of 
vestibular information. 

Dorso-lateral to the restiform body at its emergence from 
the medulla lies one reception nucleus for the cochlear 
division of the eighth nerve, while ventro-lateral to the same 
body lies a second reception nucleus (see VII in Fig. 47). 
Secondary paths from the dorsal nucleus wind over the 
dorso-lateral surface of the anterior cerebellar peduncle, 
thence across the floor of the fourth ventricle as the strise 
acusticse as far as the midline of the medulla where they 
penetrate to the opposite side, at which point a major number 
join the lateral fillet and thence to the higher centers (Fig. 
50); some of the fibers join the mesial fillet, and some join 
the posterior longitudinal fasciculus ''to assist in establishing 
reflex paths influencing the motor nerves." 

Secondary paths from the ventral nucleus pass deeply in 



the substance of the medulla, and cross to the other side. In 
the first part of their course they receive primary and sec- 
ondary fibers from both the trapezoid and superior olivary 
nuclei of the same and opposite side; thus reinforced they 
pass upward as the lateral fillet, receiving further fibers from 
the nucleus of the lateral fillet, and terminate by arborizing 
around the cells of the inferior quadrigeminate and median 
geniculate bodies. From the inferior quadrigeminate body 

M G 


Nucleus -, 
lateral I 
fillet ^ 




3 "^i^' Median geniculate 
Inferior quadrigeminate 

Visuo-auditory association fibres 

1 nucleus 


nucleus Spiral 


Fig. 50. — Diagram illustrating the interconnections between the organ of 
hearing and the brain. 

secondary paths, via Gudden's commissure, pass to the 
geniculate body of the opposite side, and yet others pass 
laterally to the thalamus. Secondary fibers from the median 
geniculate pass to the cortex of the superior convolution 
of the temporal lobe. Finally, some fibers from the superior 
olive of the opposite side pass forward to terminate around 
the nuclei of origin of the sixth, fourth, and third nerves. 

These many terminations and connections indicate that 
impressions coming in from the cochlea pass through several 



internodes to finally be perceived in consciousness in the 
temporal lobe of the brain. At the same time, correlating 
influences pass to the ocular nuclei, and a few pass to the 
higher sensory centers. 

Fig. 51. — Primary terminal nuclei of the afferent (sensor) cranial nerves 
schematically represented in a supposedly transparent brain-stem, lateral 
view. The optic and olfactory centers are omitted. (Gray.) 

One other sensory areas of reception is found in the 
brain stem, that of the fifth or trigeminal nerve. This is 
located in the mid-lateral pontine region (see V in Fig. 47, 
also Fig. 51), ventral to the superior cerebellar peduncles, 
and extending downward through the medulla as far as the 
second spinal nerve; it appears to be a direct continuation 



upward of the substantia gelatinosa of the cord. From this 
sensory reception nucleus, secondary paths pass as arcuate 
fibers to join the mesial fillet of the opposite side thereby 
ascending to the thalamus, and thence by a tertiary set to 
the cortex. Probably some of the collaterals pass to the 
motor nuclei of the fifth, seventh, ninth, and tenth nerves, 
thereby establishing reflex arcs to the facial region and asso- 
ciated structures. Other secondaries pass into the nucleo- 


Reception nu 

, -/^^^ 



Vv ^^-~---_____ 


Anterior part of the head 
Greater part of the face 




^ f "^ 

\\\ Common 





Nose, naso-pharynx, palate 




Mouth, tonsils, teeth 


To cerebellum 
Fig. 52. — Sensory distribution of the fifth nerve. 

cerebellar tract of the inferior peduncles, and thence to the 
cerebellar cortex. Possibly also collaterals of the primaries 
pass directly to the motor nuclei of the fifth, seventh, and 
twelfth nerves. Through the fifth nerve, into this reception 
nucleus come impressions of common sensation from the 
anterior part of the head, much of the face, the tragus, eye 
nose, naso-pharynx, palate, tongue, tonsils, mouth and teeth 
(see Fig. 52), 



Motor Nuclei.— In the pons and medulla the columns of 
gray matter homologous with the anterior horns of the cord 
are broken up and displaced by the intercrossing of the pyra- 
midal strands, by the fillet decussation, and by the streaming 

Cervical nerves 

Fig. 53. — Nuclei of origin of cranial motor nerves schematically represented; 
lateral view. (Gray.) 

of the cerebellar tracts. The anterior horn is split up into a 
detached head which is displaced laterally and somewhat 
to the rear, and a basal part that is displaced posteriorly 
being brought to the ventro-lateral aspect of the central 


canal. In the mesial group are found nuclei of origin of the 
third, fourth, sixth, ninth, tenth, and twelfth nerves; in the 
lateral group are found nuclei of origin of the fifth, seventh, 
ninth, tenth, and eleventh nerves (Figs. 47 and 53). These 
several nuclei are in discontinuous groups of gray matter 
instead of being in a continuous strand as are the motor 
nuclei of the cord. 

The motor nucleus of the twelfth, or hypoglossal, nerve is 
morphologically equivalent to the base of the anterior horn 
of the spinal region. It consists of a long aggregation of cells, 
lying close to the midline, and ventral to the Sylvian aqueduct 
(see Fig. 47) ; it extends from the level of the strioe acusticce 
down as far in the closed medulla as the decussation of the 
pyramids. It has commissural fibers connecting with its 
fellow of the opposite side, and fibers passing into the poste- 
rior longitudinal fasciculus for coordinating associations 
with other motor nuclei. Its cortical connection is by means 
of fibers having their origin in the opercular extremity of the 
precentral convolution (see Fig. 66) passing thence through 
the internal capsule, down the median part of the pyramidal 
tract to the nucleus level where they terminate by arborizing 
around the dendrites of the nuclear cells. Impulses pro- 
ceeding down this tract determine the action of the tongue; 
hence they are intimately related to mastication, deglutition, 
and articulation (Fig. 54). 

Motor fibers of the ninth, tenth, and eleventh nerves have 
a serial origin from two elongated groups of cells termed the 
dorsal nucleus and the nucleus amhiguus (see Figs. 47 and 
53). The dorsal nucleus extends from the mid-portion of 
the striaoB acusticce caudally and mesially into the medulla 
as far as the gracile nucleus, being ventral to the hypo- 
glossal nucleus in this lowermost portion. The nucleus 
amhiguus lies more ventral and lateral, and extends from 
the level of the entrance of the cochlear nerve to the level 
of the upper part of the pyramidal decussation. 

The efl^erent fibers of the ninth, or glosso-pharyngeal, arise 
from the uppermost portion of the dorsal nucleus, and are 
distributed to the stylo-pharyngeus muscle, conveying 
impulses utilized in deglutition and modified vocalization (see 



Fig. 54). Cortical connection is made from the gray matter 
of the lower part of the precentral gyrus, whence through 
the internal capsule, peduncle, and pons, to terminate about 
the glosso-pharyngeal nucleus of the opposite side. Local 
connections with other motor nuclei are also made through 
the posterior longitudinal fasciculus, thereby ensuring har- 
mony of coordination. 

Lateral head 



Muscles of 
palate and 

Upper part of 

geal muscles 

Muscles of 


Fig, 54. — Diagram illustrating motor activities of the ninth, tenth, eleventh 
and twelfth nerves. 

Efferent fibers of the tenth nerve (the vagus) arise from 
both nuclei caudad to the region of the ninth nucleus, and 
are distributed to some of the palate muscles, and to the 
muscles of the pharynx, esophagus, stomach and intestines 
(as far as the splenic flexure of the colon), to the larynx, 
trachea, bronchi and its subdivisions, and to the heart. The 
major portion of these fibers are not truly vagal in origin 
but are additional fibers contributed by ganglia of the auto- 
nomic system. These latter are the visceromotor, secretory, 
and inhibitory fibers to the viscera; so the true vagal dis- 
tribution is chiefly to the muscles of the palate and upper 


portion of the esophagus, and to the muscles of the upper 
portion of the larynx. A portion of the tenth nerve, arising 
in the nucleus ambiguus caudally serial with the origins of 
the ninth and tenth just described, is usually attributed to 
the eleventh nerve. In reality it is an integral portion of the 
tenth, both in origin and distribution, though temporarily 
contained in the dural sheath of the eleventh for the distance 
of a few millimeters. The distribution of these accessory 
fibers is to the lower laryngeal muscles through the inferior 
laryngeal nerve; hence the tenth nerve is intimately asso- 
ciated with all the intricate processes of vocalization (see Fig. 

The nuclei of origin of the ninth and tenth cranial nerves 
are associated with other motor nuclei of the brain-stem 
through the posterior longitudinal fasciculus; so the activities 
manifested through these nerves are intricately correlated 
with adjunct activities. Cortical connections are made 
through axons derived from cells located in the lower pre- 
central gyrus (see Fig. 66). 

The eleventh nerve proper arises from a special collection 
of cells located in the dorso-lateral region of the anterior 
horn lying between the lower end of the medulla and the 
sixth cervical segment of the spinal cord. Presumably these 
nuclei are served by the motor fibers of the pyramidal tract; 
their axons of distribution are to the sterno-cleido-mastoid 
and trapezius muscles which are concerned with lateral 
movements of the head. 

Two other exceedingly important centers are located in 
the brain-stem, though their exact anatomical boundaries 
have not been ascertained. One of these is the respiratory 
center which sends out impulses to the respiratory nerves, 
particularly to the phrenic nerve. Experimental evidence 
points to this center as consisting of a bilateral collection 
of cells lying adjacent to the mesial line in the region of the 
calamus scriptorius, and probably in close association with 
the sensory terminations of the vagus. The other center 
is the vaso-constrictor. Histologically, this center has not 
been located; but experimental evidence indicates that it 
lies in the tegmentum of the pons, mesad to the facial nucleus. 



Three different cranial nerves have their nuclear motor 
origins in the pons. These are the fifth, sixth and seventh 
nerves. The fifth, or trigeminus, nerve has its chief origin 
in the nucleus masticatorius , an oval column of cells lying 
deep in the supero-lateral area of the fourth ventricle, mesad 
to the sensory nucleus; these cells may be considered equiva- 
lent to the detached anterior horn. Accessory to this chief 
nucleus is another nucleus located lateral and close to the 

Sphinct. Pupillae| 

Sup., int. & inf. 
recti Inf. oblique 
Levat. palpeb. 

Sup. oblique 

Ext. rectus 

Muscles of the 

Ear muscles 
Post, digastric 

Muscles of 

Tensor palatl 
Tensor tympani 
Ant. digastric 

Fig. 55. — Nuclei of nerves governing facial expression. 

Sylvian aqueduct in the mesencephalon (see Fig. 53). Cor- 
tical connections are established through the pyramidal 
fibers from the lower third of the precentral convolution (see 
Fig. 66); probably there may be also some association with 
sensory efferents to the facial nucleus. The distribution of 
the impulses passing out of the motor nucleus are to the 
miicles of mastication (Fig. 55) ; and the suggestion has been 
made that the mesencephalic portion may be concerned with 
impulses passing to the tensor palati, tensor tympani, mylo- 


hyoid, and the anterior belly of the digastric; other writers 
think this mesencephalic portion is vestigial only, and even 
then is of sensory relation. 

The sixth nerve arises from a group of large multipolar 
cells lying just beneath the floor of the fourth ventricle, 
cephalad to the strice and ventrad to the eminentia teres 
(see Figs. 47 and 52). This is the nerve through which pass 
those impulses effecting lateral deviation of the eyeball (see 
Fig. 55) . The nucleus has cortical connection via the pyramid 
of the opposite side; is connected through the posterior longi- 
tudinal fasciculus with the motor nuclei of the opposite side; 
and is associated with some of the fibers of the superior olive, 
through which association there is established a direct reflex 
arc between cochlear impressions and eye movements. 

The seventh nerve arises from a large nucleus lying deep in 
the tegmentum of the pons, medial to the origin of the fifth 
nerve, and slightly above the level of the strice acusticce (see 
Figs. 47 and 52). It has a close association established 
through the posterior longitudinal fasciculus with the optic 
motor nuclei and with the auditory reception nucleus; it is 
also probably connected with the nucleus of the hypoglossal 
nerve, as indicated by the close coordination of action between 
lip and tongue. The seventh is sometimes called the nerve of 
expression since it supplies all the muscles of the face, and 
conveys the impulses associated with emotion, as well as 
those indicative of the present mental state (see Fig. 55); 
it is also distributed to the intrinsic and extrinsic musdes of 
the ear, and to the stylo-hyoid, platysma, and the posterior 
belly of the digastric muscles. 


Although small in size, the mesencephalon has in it impor- 
tant nerve tracts and centers, as well as nuclei of origin of 
some of the cranial nerves. Postero-superior are the quadri- 
geminate bodies (see Figs. 47). The superior pair serves several 
functions : They are relay stations for visual impulses passing 
from the retina to the occipital lobe; they establish sensory 
connections indirectly through the mesial fillet between the 


spinal cord below and the thalamus above; through the 
lateral fillet they serve as an internode for auditory reflexes; 
through the posterior longitudinal fasciculus they assist in 
the correlation of the sensory-visual with the motor-visual 
tracts; through the tecto-bulbar tract they are related with 
other motor areas in the stem, and with the cord through 
the tecto-spinal tract. Closely associated with the superior 
colliculi are the external geniculate bodies which serve as 
internodes for both corticipital and corticifugal occipito- 
optic fibers and impulses. 

Caudad to the superior colliculi are the inferior quadri- 
geminate bodies. These structures are internodes serving to 
connect the auditory reception nuclei with the lenticular 
nuclei of the opposite side. They also have some non- 
visual relation with the optic tract, probably with the 
afferents from the ocular muscles. Closely associated with 
the inferior colliculus is the mesal geniculate body which 
serves chiefly as a relay station for auditory impulses passing 
from the cochlear nucleus on their way to the superior 
temporal nucleus. 

In the most cephalad portion of the mesencephalon, ventro- 
lateral to the Sylvian aqueduct, are two prominent masses 
of gray matter forming the red nuclei, or nuclei of the teg- 
mentum. These nuclei are chiefly internodes connecting 
the cerebellar cortex with the cerebral cortex through the 
thalamus, and the cerebellar cortex with the cord through 
the rubro-spinal tract. Other connections with the nucleus 
are from both the cerebral cortex and from the corpus 
striatum, thus establishing an accessory motor path. 

Caudad to the red nucleus, and occupying an area in the 
Sylvian gray matter commensurate with the superior col- 
liculus, is the nucleus of the third, or motor oculi, nerve 
(Figs. 47 and 53). Impulses passing out of this nucleus are 
distributed peripherally to the following muscles of the eye: 
The superior, internal and inferior recti; the inferior oblique; 
and the levator palpebrse superioris (Fig. 55). Cortical 
impulses originate in the posterior part of the inferior frontal 
convolution just anterior to the precentral fissure (Fig. 
66). Relational connections of this nucleus for the further 


passage of impulses are as follows : Indirectly with the visual 
area in the occipital lobe by corticifugal fibers through the 
optic radiation and superior corpora quadrigemina ; through 
the posterior longitudinal fasciculus with the other ocular 
nuclei; and also with Deiter's nucleus; also, through the 
posterior longitudinal fasciculus with those cells of the facial 
nucleus supplying the corrugator supercilii and orbicularis 
jMlpehrarum muscles whereby those muscles are coordinated 
in action with the levator palpebrarum; probably also, with 
the sensory nuclei of reception for accurate adjustment of 
motor impulse to sensory need. 

Opposite the level of the inferior quadrigeminate body is 
located the nucleus of the fourth nerve, the trochlear (Figs. 
47 and 53). This lies deep in the Sylvian gray matter 
caudad to the nucleus of the motor oculi but not continuous 
with it. Impulses out of this nucleus produce contractions 
of the superior oblique muscle of the opposite side (Fig. 
55). Its bulbar relations are with the ocular nuclei, thus 
insuring harmony of coordination, and with the cochlear 
nucleus in the superior olive; these connections are made by 
means of the posterior longitudinal fasciculus. 

It may be well to summarize our present knowledge con- 
cerning the physiology of the posterior longitudinal fasciculus, 
even though some of the connections remain indefinite and 
obscure. This tract is one of the most ancient association 
bundles, as shown by its early myelination (fourth fetal 
month) . It may be traced cephalad as far as the floor of the 
third ventricle where some of its fibers have nuclei of origin; 
its connections in this region are not known, but it may 
possibly be linked up with some of the gray matter found 
early in the history of the prosencephalon. From this 
anterior origin it may be traced through the tegmentum of 
the pons, the dorsal and ventro-lateral field of the medulla, 
down into the anterior ground bundle of the cord. In its 
course it is constantly receiving and giving off fibers of 
communication and coordination, thereby establishing phys- 
iological relations with the nuclei of all the cranial nerves 
from the third to the twelfth inclusive (Fig. 56). Through 
this means reflex paths exist between the sensory and motor 



nuclei of nerves of like distribution, as well as between 
nuclei of coordinated activity. Vestibular impulses are thus 
correlated with higher and lower centers, and especially with 
the motor nuclei of the eyes. The lateral deviations of the 
eye are thus controlled through their motor nuclei; these and 
other ocular controls are coordinated with nuclei controlling 
facial impulses; others of the facial group, especially those 

Ocular adjustment 


Expression of 




Fig. 56. — Illustrating how some of the motor centers are coordinated 
through the posterior longitudinal fasciculus. 

concerned with lip action, are harmonized with the nucleus 
of the hypoglossal; this latter, in turn, with the palatal and 
laryngeal nuclei of the tenth and eleventh nerves, as, for 
example, in deglutition or vocalization. In fact, both 
clinical and experimental evidence indicates a very complex 
coordination of these cranial nuclei, a prominent factor in 
which is the posterior longitudinal fasciculus. 


The ventral portion of the mesencephalon is occupied by 
cerebral peduncles. In these peduncles three main bundles 
are distinguishable. The mesial fifth is occupied by the 
fronto-pontine tract, and the lateral fifth is occupied by the 
temporo-occipito-pontine tract, both of which are conveying 
impulses from the cerebral cortex to the cerebellum, with an inter- 
node in the pontine nuclei. Lying adjacent to the fronto- 
pontine strand is a group of fibers known as the cortico-bulbar 
tract, bearing impulses from the motor areas of the frontal lobe 
to the motor nuclei of the origins of the cranial nerves. The 
remaining portion of the peduncle is occupied by the great 
pyramidal tract passing from the precentral area of the 
cortex down into the spinal cord, and conveying volitional 
motor impulses. 


Mention has been made frequently of the many tracts 
passing to and from the cerebellum; these many tracts indi- 
cate that the cerebellum is of great importance to the welfare 
of the individual, an importance which comparative physi- 
ology indicates grows in direct relationship to the complexity 
of the animal's motor reactions. These tracts may be grouped 
as follows: 

Afferent. — (1) Subconscious sensations of touch, muscle 
and tendon tension, and joint apposition, pass to the cerebel- 
lum ma the inferior and superior cerebellar peduncles. (2) 
Vestibular sensations, and impulses from the inferior olivary 
body, are conveyed by the inferior cerebellar peduncles. 
(3) Association impulses coordinating the bulbar nuclei 
of the fifth, seventh, ninth, and tenth nerves, are conveyed 
through the inferior cerebellar peduncles. (4) Other impulses 
from both the bulbar nuclei and cortical areas having to do 
with various association coordinations are conveyed through 
the middle cerebellar peduncle. (5) Visuo-motor impulses 
from the superior quadrigemina pass probably through the 
superior peduncles. 

Efferent Tracts. — (1) Muscle-vestibular association im- 
pulses proceed from the roof nucleus through the inferior 
peduncle to the nucleus of Deiter, thence by relays to motor 



cells at different levels of the cord. (2) Impulses down to 
the olivary nucleus through the inferior peduncle. (3) 
Multitudinous association impulses through the middle 



Auditory correlation 

impulses to the 

superior quadrigeminate 

Accessory motor 
impulses through 
the red nucleus 

Visuo-motor sensations 

from the 
superior quadrigeminate 

Association impulses 

to the 

pontine nuclei 

Bulbar and cortical 
association afferents 

Association impulses 

to the 

superior olive 


association impulses to 

Deiters nucleus 

Association impulses 

from the 

5th, 7th, 9th and 10th Ns. 

Vestibular sensations 

Impulses from the 

inferior olive 

Subconscious sensations 

of touch, muscle tension 

and joint position 

Fig. 57. — Cerebellar connections. 

peduncle to the pontine nuclei, and to the frontal and tem- 
poral cortex. (4) Impulses of obscure relation— passing 
from the roof nuclei through the superior peduncle to the 


red nucleus and thence by relays through to the subthalamic 
region. (5) Impulses probably concerned with auditory 
associations passing from the central nuclei, through the 
superior peduncle, to the superior quadrigeminate body. 
(Compare the data in the two preceding paragraphs with 
Fig. 57.) 

In both experimental and clinical work it has been found 
that interference with the function of the cerebellum results 
in marked disturbances of locomotion; and that muscle 
coordinations, formerly performed automatically, now labori- 
ously ensue from a direct effort of will, and not as precisely 
and promptly as before the injury took place. Such data, 
together with deductions gathered from known neural 
connections and associations, admit of a summarizing of the 
junctions of the cerebellum somewhat as follows : 

1. The cerebellum is a great coordinating ganglion con- 
trolling what Sherrington calls the ''proprioceptive" system. 

(2) It furnishes the cerebral cortex with systematized 
information for appropriate determination of motor impulses. 

(3) By means of its reception of muscle sensation, and its 
connection with the vestibulo-spinal tract, it serves to 
greatly heighten the tonicity of all the muscles of the body. 

(4) Through this same muscle sensation receptivity, in con- 
junction with afferent impressions from the labyrinth, it 
serves to coordinate bodily posture with cranial position. 

(5) It thus serves to adapt the organism to its position in 
space, especially in relation to the organism's center of 

The influence of the cerebellum on musculature of the 
body is homolateral, while the relation of the cerebrum to 
the cerebellum is contralateral. 


Bounding the third ventricle on each side in its posterior 
three-fourths, is a large elliptical mass of gray matter known 
as the oi^tic thalamus (Fig. 61A); this structure is free 
on its dorsal and mesal aspects but is continuous with adjoin- 
ing structures on its other faces. The thalamus is "a. great 



ganglionic internode interposed in the cortieipetal paths" 
of most of the afferent impulses coming from the spinal cord, 
cerebellum and brain stem. Sensor}' impulses coming in 
from all parts of the body are here switched by relays of 
axons to specialized portions of the cortex for conscious 
perception, or to secondary ganglia for subconscious inte- 

Impressions of 

touch, pressure, 

muscle tension, 

temperature, pain 

Ocular sensations 

Olfactory impressions 

Impressions from 
sensory nuclei 
In brain stem 

impressions of 


Fig. 58. — Connections of the thalamus. 

gration and utilization. To it come also fibers and impulses 
from all parts of the cerebral cortex, and from it descending 
fibers pass to the brain stem and spinal cord. The principal 
ascending afferent tracts are those passing from the spinal 
cord, bearing impulses of touch, temperature, pain, pressure 
and tension, chiefly; those passing via the median fillet from 



the various nuclei of the brain stem, conveying associated 
impressions; those passing via the cerebello-thalamic or the 
cerebello-rubro-thalamic tract, conveying impressions chiefly 
associated with equihbration and locomotion; impressions, 
possibly subliminal, from the optical tract and from the 
olfactory bulb. Impressions from sensory areas coming 
through the thalamus are relayed to appropriate cortical 
areas, the principal radiations being to the frontal, parietal, 





Fig. 59. — Mesal aspect of a brain sectioned in the median sagittal plane. 


and occipital lobes; from these same areas, return communica- 
tions are made with the thalamus, thereby indicating a 
remarkably complex and intricate association (Fig. 58). 

Supero-posteriorly, above the quadrigeminate body, is the 
pineal body (Fig. 59), a rudimentary structure of no known 
present function. Antero-inferiorly is the 'pituitary body 
(Fig. 59), with its double origin from the nervous system 
and from the stomatodoeum. The posterior nervous portion 
seems to be rudimentary; the much larger anterior part has 



some obscure relation with the function of growth; the pars 
intermedia is related to the tonicity of smooth muscle. 

The telencephalon contains, deep in its infero-lateral 
area opposite the thalamus, two large aggregations of gray 
matter, sometimes termed the basal ganglia; and two modi- 





Fig. 60. — Schematic representation of the chief ganghonic categories (I to V). 


fied portions of the cortex, the optic tracts and the olfactory 

The basal ganglia are also known as the corpora striata; 
they consist of two parts known as the lenticular, or lentiform, 
nucleus and the caudate nucleus (Figs. 60, 61 and 62). 



The striate body receives fibers from the optic thalamus, the 
inferior quadrigeminate, and from the olfactory tract, and 


I Lateral ventricle 

Caudate nucleus 
Internal capsule 

Lentiform micleus 

Claii-^ti I'm 

Corpus callosum 
Choroid ylexiia of 
lateral ventricle 

Choroid plexus of 
third ventricle 

Third ventricle 

Red nucleus 

Substantia nigra 
Post. perf. substance 

Base of peduncle 
Nucleus of Luys 
Taenia hippocampi 

Inferior cornu of lateral ventricle 

Fig. 61. 

Gyrus dentatus Caudate nucleus 
-Coronal section of brain immediately in front of pons. (Gray.) 

sends fibers to the thalamus, the red nucleus, and the pos- 
terior longitudinal fasciculus (Fig. 63). These connections 
indicate that the striate body is an independent ganglionic 



structure, concerned in some way with sensory-motor reflexes 
of an order lower than those depending on cortical modifica- 
tion, i. e., subconscious reflexes. Disease of the lenticular 
nucleus gives symptoms characterized by rigidity and tre- 
mors in both extremities with marked interference with 

Fig. 62. — Two views of a model of the striatum: A, lateral aspect; B, mesal 


voluntary coordinations, defects of articulation and degluti- 
tion, sometimes spasmodic laughing and weeping, with occa- 
sional marked prolongation of the beginning and ending of 
contractions of the facial muscles. This group of symptoms 
indicates that these nuclei are intimately concerned with 



those muscle coordinations having to do with the welfare of the 
organism as a whole; they are very ancient masses of gray 
matter, being among those areas first formed in the cephalic 
end of the animal. 

As noted in the brief discussion of the evolution of the 
nervous system, early in the development of the prosenceph- 
alon, there develops laterally the two optic stalks. The ante- 




=:=-. 1 ^ 


1 Corpus \ 
I striatum / 


Fig. 63. — Connections of the striate body. 

rior portion becomes encupped and ultimately forms the 
retina of the eye. Axons from the retinal cells pass back 
from the primitive stalk, but soon unite with their fellows 
to join the optic chiasm, in which commissure the fibers 
from the mesal halves of the retinae pass across to unite with 
the fibers from the outer half of the opposite side to form the 
optic tracts. These tracts curve around the cerebral peduncle 
to terminate as follows: The outer side in the pulvinar of 


the thalamus, the middle part in the lateral geniculate and 
the superior quadrigeminate, and the mesal portion in the 
inferior quadrigeminate, and the median geniculate. Secon- 
dary fibers arise in the thalamus and lateral geniculate and 
pass backward to the cuneate division of the occipital lobe; 
these fibers convey impulses concerned with vision. The fibers 
terminating in the superior quadrigeminate are in close 
association with the oculo-motor centers, and serve to secure 
coordination of retinal impressions and ocular adjustments; 
and with cochlear impressions coming through the lateral 
fillet, which coordinate auditory impressions and ocular ad- 
justments; and with vestibular impressions coming through 
the posterior longitudinal fasciculus, which give coordination 
of retinal impressions and equilibrium impressions. The 
mesal, fibers coming from the inferior quadrigeminate are 
commissural fibers relating to auditory sensations, and are 
not concerned with visual impulses. 

The crossing of the fibers in the chiasm gives conjugate 
unilaterality to the transmittal of impulses, the right or left 
field of vision being received respectively on the left or right 
side of the cortex of the brain; but the sensations thus pro- 
duced in the cortex are homogeneous. 

From the superior quadrigeminate secondary fibers pass 
down to the oculo-motor centers, thereby admitting of close 
reflex coordination between the muscles controlling the eye 
and the peripheral sensations of sight. 

Efl^erent fibers passing from the cortex to the retina have 
also been described; these assumedly have some vasomotor 
effect on the retinal bloodvessels. There are also some very 
fine afferent fibers from the retina which may possibly con- 
vey to the oculomotor center impulses from the pupillary 

The peripheral percipient area of the olfactory apparatus 
is located in the roof of the nasal cavity, extending along 
the mesial surface of the superior turbinate bone and an 
adjacent part of the nasal septum. The olfactory cells here 
located send their axons through the cribriform plate of the 
ethmoid bone to terminate in arborizations around the 


dendrites of the mitral cells in the olfactory bulbs; these 
bulbs, it will be recalled, are rudiments of the primitive 
olfactory lobes. The axons of the mitral cells carry the 
impulses cortexward by relays to ultimately terminate 
principally around the uncinate division of the hippocampal 
lobe and in the amygdaloid nucleus of the same side, though 
a few fibers pass over to the opposite side through the anterior 
commissure. There are other terminations in the dentate 
convolution, adjacent to the region of the descending horn of 
the lateral ventricle, but the present physiological significance 
of these fibers has not yet been determined. 

Association fibers are known to connect the uncus with 
the thalamus; and other widespread associations are assumed, 
especially in relation to the sense of taste. 


Because of the close affiliation of the cranial fibers of 
the autonomic system with the distribution of some of the 
cranial nerves, and because of errors of reference easily 
arising from unusual stimulation of the afferent fibers of the 
sympathetic system, it seems best to discuss the physiology 
of the autonomic system before taking up the physiology of 
the cerebrum. 

The autonomic system is conveniently grouped in reference 
to the anatomical locations of its nuclei as follows: Tectal 
autonomics, having to do with the ocular distribution; 
bulbar (or medullary), and sacral autonomics, concerned 
principally with motor and secretory distributions along the 
alimentary tract, or its embryonic diverticulae ; thoracic 
autonomics, related largely to the vascular condition of the 
abdominal viscera; and enteric autonomics, concerned with 
the automatic activity of the stomach and bowels. The 
fibers of this system are- distributed exclusively to smooth 
muscle, to cardiac muscle, and to glandular tissue. 

There are four areas in the central nervous system where 
autonomic fibers take origin: the mesencephalon, or mid- 
brain, medulla, first thoracic to fourth lumbar, and the 
sacral region. 

The autonomic fibers arising in the mesenseyhalon leave 
the brain with the third nerve, passing to the ciliary ganglion 
where they terminate in arborization around the dendrites 
of secondary or ganglion cells whose axons (as postganglionic 
fibers) pass to the smooth muscle of the sphincter of the iris 
and to the ciliary mucle. Hence, neural impulses passing 
along these fibers produce a myotic pupil, increased intra- 
ocular tension, and hyjjermetropia. 



The more anterior autonomic fibers arising in the medulla, 
probably from cells homologous with the lateral motor horns 
of the cord, leave the brain with that part of the seventh 
nerve, called the nerve of Wrisberg. These fibers separate 
from the seventh nerve as the chorda tympani branch; 
they supply vasodilator and secretory impulses to the sub- 
maxillary and sublingual glands, in which distal areas are 
located the peripheral ganglia (Fig. 64). From the seventh 
nerve also pass fibers to the spheno-palatine ganglion whence 

Medullary Centre 
Nerve VII 
Nerve IX 

Parotid GlancT 

Otic Ganglion 

lingual Gland 
Submaxillary Gland 
Sublingual Ganglion 

Nerve V 
Superior Cervical Ganglion 

Fig. 64. — Innervations of the salivary glands. 

postganglionic fibers pass with branches of the fifth nerve to 
supply secretory and vasomotor impulses to the mucous 
membrane of the nose, soft palate, and superior portion of the 

More caudad in the medulla other fibers leave the brain 
with the ninth nerve to pass to the otic ganglion, thence as 
postganglionic fibers to convey secretory and vasodilator 
impulses to the parotid gland, (Fig. 63), and vasodilator 
impulses to the back of the tongue. 



Slightly more caudad still arise other autonomic fibers that 
accompany the vagus nerve to supply visceromotor fibers 
to the esophagus, stomach, small intestine, and the major 
portion of the large intestine; secretory fibers to the glands 
of the stomach and pancreas; motor fibers to the muscles of 

Fig. 65. — Diagram illustrating the path of a simple reflex in the autonomic 
system; dotted line = afferent or sensory fibers, the unbroken line — the 
efferent or motor fibers. A, Spinal cord; B, lateral horn; C, sensory root; 
D, motor root; E, ganglion on sensory root; F, gangliated cord of autonomics; 
G, autonomic ganglion; H, visceral nerve. 

the bronchi ; inhibitory fibers to the heart, and possibly to the 
pyloric and ileo-colic sphincters. 

That part of the autonomic system comprised in the tho- 
racic group has its origin in the lateral columns of the anterior 
horns of gray matter from the second dorsal to the third or 


fourth lumbar segment; these fibers pass out with the motor 
roots to enter the bilateral gangliated cord as white rami; 
they may then terminate in an adjacent ganglion, or one 
more remote, or may pass through to proceed to one of the 
great supravascular ganglia, or even on to some of the 
minute terminal ganglia, having in any case but one relay 
no matter which may be the designated ganglion (Fig. 65). 
In the cervical region there are usually but two ganglia, 
the superior and inferior cervical, both of which are con- 
nected caudally with the stellate ganglion lying just caudad 
to the level of the left subclavian artery. From the ganglia 
of the gangliated cord, gray rami return to the spinal nerve, 
joining both the anterior and posterior divisions of all the 
spinal nerve roots ; with these spinal nerves, they are distrib- 
uted to the periphery where they supply vasomotor and 
pilomotor impulses to involuntary muscle, and secretory 
impulses to glandular structures— all in the somatic area, 
including some to the spinal meninges. 

The cervical segments give off no white rami, the auto- 
nomics for the cervico-cephalic region being derived from the 
rami of the first to sixth dorsal, whence they proceed to the 
stellate ganglion, then to the inferior cervical, then to the 
superior cervical. 

The superior cervical ganglion, composed of the fusion 
of three or four separate ganglia, lies opposite the second 
cervical vertebra, dorsal to the internal carotid artery, and 
mesal to the vagus nerve; the inferior cervical ganglion lies 
opposite the level of the transverse process of the seventh 
cervical vertebra. These ganglia, including the middle 
cervical ganglion when present, are connected by the sym- 
pathetic cord, and give ofl^ the following supply: 

1. Vasomotor fibers to the bloodvessels supplying the 
scalp, meninges, face, eye, pituitary and thyroid, neck and 
upper extremities, and mucous membranes of the head. 

2. Pilomotor fibers to the integument of the head, neck 
and upper extremities. 

3. Motor fibers to the involuntary muscles of the eyelids 
and orbit, and especially to the dilator muscle of the iris. 


4. Secretory and vasoconstrictor fibers to the salivary glands 
and to the muciparous glands of the nose, throat and pharynx, 
to the lachrymal glands; and to the sweat glands of the head, 
neck, and upper extremities. 

5. Accelerator or augmentor fibers to the heart. 

6. Communicating (coordinating?) branches to the third, 
fourth, fifth, sixth, ninth, tenth, twelfth, and phrenic nerves. 

7. Vasomotor fibers to the subclavian and mammary 

8. Vasodilator fibers to the face, neck, and to the cephalic 

The splanchnic, or abdominal, or visceral portion of the 
sympathetic, is derived from fibers coming from the fifth 
dorsal to the third lumbar segments of the cord. In the 
thorax these fibers supply vasomotor impulses to the aorta, 
and to the bloodvessels of the lungs; and visceromotor fibers 
to the bronchial dilators. In the abdomen these fibers 
supply, by means of the splanchnic nerves and collateral 
plexuses and ganglia, the following: 

1 . Viscero-inhibitory impulses to the stomach and intestines. 

2. Visceromotor impulses to the ileo-colic sphincter, 
the sphincter pylori, and inner sphincter of the anus. 

3. Secretory fibers to all the abdominal viscera, except the 

4. Vasoconstrictor fibers to all the branches of the abdom- 
inal aorta. 

5. Vasodilator fibers to the stomach, liver, spleen, kidneys, 
and intestines. 

6. Secretory fibers to the adrenals, ovaries, and testicles. 
This splanchnic area also contains a large number of 

afferent fibers bearing sensory impulses from the abdominal 
area into the posterior root of the spinal cord; the most of 
these impressions probably pass directly to the lateral horn 
and there arouse autonomic motor impulses. When the 
impulses are unusually strong, they induce secondary 
impulses that proceed up to higher centers, not infrequently 
attaining the sensorium. 
In the walls of the stomach and intestines, lying between 


the muscular coats, are the extensive plexuses of Auerhach 
and Meissner which form the enteric group of autonomics. 
These plexuses are primitive, diffuse neuro-fibrillar systems 
capable of responding to stimuli from the intestinal mucosa 
in a coordinated manner. Their activity is independent of 
impulses from the central nervous system, though such 
activity may be greatly modified by stimuli entering by 
either the vagus or splanchnic route. These plexuses are 
assumed to be the factors controlling the several movements 
taking place in the musculature of the alimentary tract. 

The Lumbar portion of the gangliated cord consists of 
four small ganglia lying anteriorly to the lumbar vertebra, 
connected with the thoracic and sacral portions by commis- 
sural cords, and having both white and gray rami. The 
somatic portion joins the anterior and posterior spinal divi- 
sions for distribution as vasomotor, pilomotor, and secretory 
fibers to the lower extremities. The visceral distribution 
includes vasoconstrictor fibers to the bloodvessels of the lower 
abdomen and pelvis including the cavernous structures; 
motor fibers to the descending colon, vesical sphincter, uterus, 
vagina, and circular muscles of the rectum and bladder; 
inhibitor fibers to the longitudinal fibers of the rectum and 

The Sacral portion of the gangliated cord consists of two 
portions, a somatic part receiving its fibers from the lumbar 
cord, and a visceral part consisting of the sacral white rami 
which join in a single large pelvic nerve sometimes called 
the nervus erigens. The somatic part supplies the caudal 
region with vasomotor, pilomotor and secretory branches. 
The visceral portion sends branches to the pelvic plexuses 
where they are joined by hypogastric branches from the 
lower splanchnic area, and are then distributed as follows: 
Motor branches to the vas deferens, seminal vesicles, prostate, 
and the longitudinal muscles of the rectum and bladder; 
inhibitor fibers to the vesical sphincter and the circular 
muscles of the rectum and bladder; vasomotor fibers to the 
uterus and vagina; vasodilator fibers to the corpora cavernosa 
et spongiosa, and the vestibule. 


In discussing the physiology of the voluntary nerves men- 
tion was made of the balanced action of the flexor and 
extensor groups of muscles whereby action of one group 
simultaneously inhibited the tonicity of the opposed group. 
An analogous condition seems to prevail in the autonomic 
nervous system whereby both the cranial and sacral divisions, 
called the parasympathetic, are antagonized by the sympa- 
thetic. The cranial division is largely concerned with build- 
ing up of bodily reserves, for the protection of the system 
in times of need; it also serves to conserve the strength of the 
heart and lungs. The sacral division has two main functions : 
(a) The furtherance of racial continuity, and (6) the securing 
of relief from distention of the several pelvic viscera. The 
sympathetic division, while also concerned with several 
important anabolic processes, is of vital importance in 
preserving the individual in times of grave emergencies. 
If occasion arises requiring the output of great amounts of 
energy, as in flight from danger, or in repelling bodily assaults, 
then the sympathetic system responds with great power, 
at the same time inhibiting the cranial and sacral divisions. 
As a consequence, those areas supplied by the sympathetic 
will show preponderance of action. The pupils will dilate; 
the hairs, especially of the spinal region, will tend to stand 
on end; the heart will beat more rapidly and forcefully; 
the bronchial muscles will relax, permitting of accelerated 
movement of air; the abdominal viscera will cease their 
rhythmic and peristaltic activities; the splanchnic blood- 
vessels will be constricted, and the excess blood will be 
driven to the muscles for emergency duty. At the same 
time the adrenals are stimulated, and the presence of their 
added secretion to the blood stream increases the splanchnic 
vasoconstriction, with resulting augmented distribution of 
the blood to the heart, lungs, central nervous system, and 
voluntary muscles; it acts further on the glycogenolytic 
function of the liver so as to flood the blood with sugar for 
immediate availableness to the muscles; it also hastens the 
blood through the muscles, thereby facilitating the removal 
of katabolites and thus postponing the onset of fatigue; 


furthermore, in some as yet unexplained manner, it induces 
a more sensitive coagulability of the blood. All of these 
reflexes resulting from sympathetic activity serve to protect 
the organism in moments of great emergencies, besides 
rendering response more effective. 

The autonomic system seems to be concerned solely 
with a control of the unconscious coordinated actions of the 
body, the so-called vegetative processes— the movements of 
the heart and unstriated muscle and the activities of the 
glandular structures. So far as is known, the autonomic 
nerves are not controllable directly by the will, there being 
no apparent connection between their nuclei of origin and 
the motor area of the cortex. But though the will can 
seemingly exert no direct influence, yet the sympathetic 
system is remarkably responsive to emotional conditions, 
possibly because of the evolutionary relationship between 
the autonomic system and the emotional response (see 
page 227) . This interrelation is very extensive, and probably 
exerts an influence on the animal economy far more profound 
than is commonly recognized, especially in individuals of 
relatively unstable temperament. Emotions which are 
associated with conserving activities will be manifested 
mainly through the cranial division; those dealing with 
conservation of the race, through the sacral division; those 
correlated with protection of the organism from imminent 
destruction are manifested mainly through the s^Tupathetic 
division. This last group is usually referred to as the major 
emotions, and consists of such emotions as fear, pain, and 
rage; each of these produce a splanchnic stimulation with all 
the systemic corollaries indicated above in the discussion 
of splanchnic activity. Thus fear and rage inhibit the auto- 
nomic reflexes of the cranial and sacral divisions w^hile greatly 
stimulating those of the sympathetic division; in such a 
condition, gastric and intestinal activity are inhibited, the 
heart is accelerated, blood-pressure is heightened, blood 
volume in heart, lungs, nervous system and voluntary muscle 
is increased, and adrenal activity with its extensive conse- 



quences is promoted. All of this subserves the purpose of 
action, and gives markedly augmented energy to that action; 
and thus may exert a true dynamogenic influence. When, 
however, this reflex does not eventuate in adequate action, 
an abnormal condition may supervene, the consequences of 
which will depend on the intensity of the emotion, its dura- 
tion, or the sensitiveness of the body in response. Many a 
perversion of function, a neurasthenia, a hysteroid state, 
or a depressive insanity even, may be traced to emotional 
excesses, or aberrant suppressions of emotions, with con- 
current or consequent splanchnic instabilities. These unfor- 
tunate eventualities may have their first development in a 
disordered function, as of the stomach, in which digestion as 
well as motility is inhibited by some anxiety (which is but 
anticipatory fear) ; from such a function disarrangement there 
is provoked a vicious circle with all its attendant evils. 

It may not be assumed that these reactions are rigidly 
universal, since to a considerable extent they are influenced 
by the individual temperament. The reflex response is not 
identical in all individuals, the splanchnic area being more 
sensitive in some than in others. In not a few people, fear, 
or even anxiety, produces increased peristalsis rather than 
decreased; in some, also, fear seems to paralyze power rather 
than increase it, the vasodilator action in such cases seeming 
to predominate over the vasoconstrictor. 

Following is a tabular summary of autonomic antago- 


Bulbar, via tenth 

Splanchnic sympa- 

Lumbar sympa- 

Plexuses of Auer- 
bach and Meissner; 
augmented by vagus. 

Point of action. 

(Esophagus, stomach 
small and large intestine. 

Pyloric, ileo-colic and 
internal anal sphincters. 

Descending colon, sig- 
moid, circular muscles of 
rectum, bladder; vesical 
sphincter, uterus and va- 

Intestinal peristalsis. 


Splanchnic sym- 

Bulbar, via tenth 

Sacral, via Nervus 

Splanchnic sym- 




Point of action. 


Sacral, via Nervus 

Longitudinal muscles 

Lumbar, via hypo- 


of rectum and bladder; 
vas deferens, seminal ves- 
icles, prostate. 


Tectal, via third 

Sphincter of iris. 


Cervical sympa- 

Dilator of iris. 


Bulbar, via tenth 

Bronchial musculature. 

Thoracic sympa- 



Cervical sympa- 


Bulbar, via tenth 

thetic (augmentor) . 



Point of action. 


Bulbar, via seventh 


Cervical sympa- 


Mucosa of nose, palate, 
and upper pharynx. 


Cervical sympa- 

Back of tongue 

f Bulbar, via ninth 


Parotid gland 


Sublingual gland 

Bulbar, via seventh 

Submaxillary gland 

1 nerve. 

Cervical sympa- 

Scalp and meninges 

/ Cervical sympa- 


Face and neck 
Upper extremities. 
Pituitary and thyroid. 
Subclavian and mam- 
mary arteries. 

\ thetic. 

Splanchnic sym- 

Aortic arch. 

Splanchnic sym- 


Pulmonary vessels. 


Splanchnic sym- 

Abdominal vessels. 

Splanchnic sym- 


Abdominal viscera. 


Lumbar sympa- 

Vessels of lower abdo- 


men and pelvis. 

Sacral via Nervus 

Uterus and vagina. 


Lumbar sympa- 

Erectile structures of 

Sacra, via Nervus 


pelvic area. 


Sympathetic via 

Skin, muscle and joints. 

Sympathetic via 

gray rami. 

gray rami. 

Appended is a table summarizing the functions of the 
autonomic nervous system: 


Parotid gland. 
Submaxillary gland. 
Sublingual gland. 

Naso-oral mucosa. 
Skin of face. 
Skin of neck. 
Internal genitals. 









Skin of face 
Skin of neck 
(Naso-oral mucosa) 

Parotid gland 
Submaxillary gland 
Sublingual gland 

External genitals 
Internal genitals 



Pyloric sphincter 

Gall-bladder, longi- 
tudinal muscles 

Gall duct, longitudi- 
nal muscles 

Muscles of bronchi- 


Intestine — as far as 
splepic flexure 

Large intestine, lon- 
gitudinal muscles 

Bladder, longitudinal 

Large intestines, cir- 
cular muscle 
Anal sphincter 
Bladder, circular 







CO o 


Muscles of bronchi- 


Small intestines 

Gall duct, circular 

Gall-bladder, circular 

Dilator muscles of iris 

(Cardiac sphincter) 
(Pyloric sphincter) 
Gall duct, longitudi- 
nal muscles 
Ileo-colic sphincter 
Large intestine, cir- 
cular muscles 
Anal sphincter 
Bladder, circular 

muscles - 
Trigone of bladder 
Internal genitals 
Hairs of skin 

Large intestine, longi- 
tudinal muscles 

Bladder, longitudinal 


Naso-oral mucosa 
Parotid gland 
Submaxillary gland L 
Sublingual gland perous 
Thyroid gland 
Pituitary gland 

Lachrymal gland 

Submaxillary gland 1 

Sublingual gland /"^^««"« 



Accessory genital glands 

Sweat glands 


1 o 












Mesencephalic Group. 

Motor: Tonic with emotions of quiet satisfaction and 
Medullary Group. 

VamdiJafnr [Pleasurable anticipations, especially gas- 
Visceromotor] tronomic.^ 

Inhibitor: Normally tonic; excess action momentarily in 
Thoracico-cervical Group. 
Motor: Dilator to eye in fright, horror, rage. 

Augmentor to heart in intense emotion or excitement. 
Vasoconstrictor: Terror and emotions involving sense of 

Vasodilator: Exaggerations of self-consciousness (shame, 
guilt, embarrassment) . 
Anticipations (pleasure, anxiety). 
Self-preservation (relative, as in jealousy, resentment, 
anger) . 
Secretory: Gastronomic anticipations. 
Splanchnic Group. 

Visceroinhibitor ] Anxiety, fear, anger, rage; excite- 

Vasoconstrictor [ ments which involve aggressive- 

Secretory to adrenals] ness. 

Vasodilator: Profound shame or embarrassment, horror, 
pain, and fear (with some people). 
Lumbar Group. 

Visceromotor (bowel and bladder) : Anxiety, fear. 
Visceromotor (uterus) : Great anxiety or grief (some 

individuals) . 
Vasoconstrictor {corpora cavernosa et spongiosa) : Altruistic 
emotions. Anxiety, shame, disgust, anger. 
Sacral Group. 

Vasodilator {gtmt&l) ^ 1 Emotions as- 

Visceromotor (genital glands, non-gonadial) 

■ sociated with 


Gray Rami Distribution. 

Pilomotor: Great fear or rage (involving bodily safety). 

Secretory: Anxiety, fear. 

Vasoconstriction: Anxiety, fear (in some individuals). 
Vomiting Center. 

Great anxiety, fear, disgust (in some individuals). 
Heat Regulating Mechanism. 

Temporarily disturbed by any strong emotion. 


Mention has been made previously of afferent fibers in 
the splanchnic nerves; there are also afferents in many of the 
other autonomic distributions, especially in those supplying 
the pelvic viscera. These afferent fibers are constantly bring- 
ing in impressions from extensive distributions, and these 
impressions induce a readjustment of the organism's several 
mechanisms to the immediate demands; these adjustments, 
moreover, are normally made in an adequately coordinated 
manner, for example, vascular caliber is constantly being 
adapted to varying cardiac force and frequency. 

For the most part, these impressions remain below the 
threshold of consciousness, though they may readily so 
increase in intensity as to produce an awareness in conscious- 
ness, as for example, in the case of accelerated peristalsis; 
or, when consciousness is in partial abeyance, as in sleep, 
the autonomic afferent impressions may influence the sub- 
merged consciousness to such a degree as to materially 
modify the phantasmagoria of dreams.^ 

Afferent impressions from the autonomic distributions 
have a pronounced influence also on the present emotional 
state, and thence inevitably on the intellectual state. The 
most evident of such examples is the reversible reactions of 
the erigenic emotions and functions, which, if uncontrolled, 

1 A fundamental error in the vagaries of the Freudian cult is the gratuitous 
assumption that the afferents from the sacral division only have any influ- 
ence on the dream state; the fact is, however, that afferents from any area, 
autonomic or otherwise, may give direction to the current of dreams'. (Se? 
Dreams, p. 224). 


are the source of much misery and degradation to both the 
individual and to society. 

The distant reflexes possible through the autonomic 
system is a subject concerning which not much is known, 
though considerable is surmised. Because of the interrela- 
tions of the several ganglia and plexuses it seems highly 
probable that efferent impulses are liable to be diffusive; 
and that the reflexes induced by afferents are not exactly 
specific. An illustration may be seen in the way gastric 
irritation sometimes indirectly reduces vagus control of 
the heart, with resulting tachycardia and anxiety; and 
clinicians are more and more of the opinion that many obscure 
symptoms are not due to immediate organic lesions but are 
functional aberrations induced by some more or less distant 
trouble in an organ obscurely related through some auto- 
nomic associations. 

This theory is rendered ever more probable by the known 
difficulty in referring exactly any given sensation arising 
from the autonomic distribution, and by the assumed 
explanation of this phenomenon. Though, normally, visceral 
sensations do not rise into consciousness, yet an undue sensa- 
tion is readily perceived in consciousness even though its 
reference is poorly localized. In fact such a sensation is not 
uncommonly referred to some cutaneous area of greater or 
lesser remoteness from the part affected. For example, 
excessive impressions arising in the costo-diaphragmatic 
reflection of the pleura are usually referred to the skin area 
over the acromion of the same side; or undue impressions 
coming from the cortical portion of the ovary may be referred 
to the lateral aspect of the thigh. The number of these 
misreferred sensations is considerable, and quite remarkable 
in their divergence of location. 

The theory offered for such misreference is that excessive 
impressions coming in through an autonomic afferent tend to 
diffuse to other structures in the same spinal segment of 
reception, thereby inducing secondary stimuli in the higher 
peripheral afferents. And since the impressions normally 
coming in from peripheral afferents are readily perceivable 
in consciousness, such latter impressions will inevitably 


have an established precedence in consciousness, and cogni- 
tion of them will inhibit largely any apprehension of the lower 
impression. Therefore the induced impression occupies the 
field of attention, and the mind refers the sensation to the 
customary peripheral area. Such being the case, it is very 
desirable that the physician should know all such discovered 
areas of reference. 

Now if an afferent autonomic impression can thus over- 
flow to a cutaneous sensory nerve, there is a justifiable pre- 
sumption that a similar diffuseness is possible in the elements 
of the autonomic system itself, with unexpected resultants in 
the efferent reflexes ; as, for instance, when a distended rectum 
or bladder induces a reflex sacral vasodilatation, or when 
gastric disorder reflexes disturb cardiac action. Thus it is 
that a physician in making his diagnoses, is liable to encounter 
both perplexing symptoms and aberrant manifestations; 
and is likely to fall into error unless he takes judicious esti- 
mation of the far-reaching ramifications and interrelations 
of the autonomic nervous system. 


Much experimental investigation indicates that there 
are in the spinal cord coordinating centers controlling various 
reflexes. But no groups of cells delimiting such centers have 
been isolated, so it is possible to indicate approximate loca- 
tions only. Thus, centers assumed to exert control over the 
pelvic functions of micturition, defecation, seminal ejacula- 
tion, and parturition, are usually located in the lumbo-sacral 
region of the cord; but an experiment by Goltz, wherein the 
whole of the cord of a female dog was removed, showed that 
the structures involved in the reflexes were capable of recover- 
ing their tone after the operation and of acting thenceforth 
in a way approximately normal, though there was a distinct 
lowering of the normal adaptability of those structures. 
However, as the animal scale ascends, it would seem that 
there is a progressive shifting of modifying influences 

Some of the more important reflexes may be enumerated: 


Tendon Reflexes.— VsiieWduY and calcaneous, each of which 
is induced by a slight tapping of the stretched tendon. 

Cutaneous Reflexes.— Vld^nidj:, cremasteric, abdominal, 
in each of which a muscle response is induced from a light 
cutaneous irritation; thus, the toes are flexed when the sole 
of the foot is tickled, the cremaster muscle contracts when 
the mesal surface of the thigh is scratched, and the oblique 
muscles of the abdomen contract when the overlying skin is 
sharply stroked. 

These several reflexes are tentatively located in the 
dorsolumbar region of the cord. Another important reflex 
is the photic, whereby the pupil dilates in response to les- 
sened variations of light; some investigators have assumed 
this reflex to be located in the first dorsal segment of the cord, 
while others would place it near the contractor nucleus in the 
mesencephalon. Another peculiar reflex is that whereby 
the pupil slightly dilates when the side of the neck is sharply 


The cerebrum as a whole has three main functions: (1) 
The registration of sensory impulses; (2) the association, 
correlation, and integration of sensory impressions; (3) the 
purposive determination of associative motor reflexes. To 
a limited extent it is possible to locate the areas in the brain 
concerned with the first and third functions; but only indef- 
initely and somewhat generally concerning the second func- 
tion. Cerebral reactions are not simple but are exceedingly 
complex. Involved in any intellectual process are a great 
number of cognitions of various sensory impressions, both 
near and remote. Thus no single portion of the cortex is 
an independent organ, but by means of multitudinous asso- 
ciation tracts it is closely connected with all other portions 
of the cerebral cortex. So it is that a visual percept, for 
example, will be associated with the percepts of varying 
muscle tensions; these will be modified by memories of more 
or less pertinent percepts derived from similar and related 
sense areas; all of which may unite to determine the quality 
of the motor response. So while it is possible to select a 
certain gyrus, and say herein is located visual percipiency, it 
is not correct to assume that this limited area has exclusive 
dominion over that particular intellectual process. This 
interdependence of the sense areas will appear more later. 

About the fissure of Rolando, or central fissure (Figs. 
66 and 67), are located the best-known areas of the 
brain. Posterior to the fissure, the cutaneous sensory area 
occupies the postcentral gyrus, extending from the fissure 
of Sylvius below to the vertex and over on the mesial aspect 
as far as the callosal gyrus. In the inferior parietal area 
is located the musculo-sensory section, concerned chiefly 



with the memory of muscle movements and tensions. Closely 
related to these two areas is the motor area of the precentral 
gyrus, extending from the Sylvian fissure below to the vertex, 

Fig. 66. — Principal fissures and lobes of the cerebrum viewed laterally. 


Fig. 67. — Lateral view of left cerebral hemisphere, showing localization of 
functions. (Gray.) 



and inesially forward an uncertain distance on the marginal 
gyrus. In this i)re-Rolandic area are located motor areas 
controlling all voluntary muscle activity, the order or arrange- 
ment being as indicated on the accompanying illustration 
(Fig. 67). 

The center for motor speech is located in the convolution 
of Broca, occupying the posterior part of the third frontal 
convolution on the left side of the brain (in right-handed 
people) ; lesions in this area produce inability to express one's 

Fig. 68. 

■Diagram showing the language zone. The opercula are divari- 
cated to expose the island of Reil. (Gray.) 

mental concepts in words, probably because there is involved 
loss of the memory of those muscle movements essential for 
articulation (Figs. 67 and 68). Memory for the sounds of 
words is located in the first left temporal convolution; 
lesions in this area result in an inability to apprehend the 
sounds indicative of speech. The center for memory of 
printed words is located in the angular gyrus; lesions in this 
vicinity produce an inability to apprehend the written or 
printed symbols of communication, though spoken symbols 
are understood without difficulty (Figs. 67 and 68) . A writing 


center is also said ta exist in the posterior part of the second 
left frontal convolution; lesions in this area are said to 
be followed by inability to form the written or printed 
symbol. These several areas are not well defined; in fact 
some physiologists doubt the accuracy of any assumed locali- 
zation, but much clinical and experimental evidence seems 
to indicate the existence of such areas in the approximate 
neighborhoods described. It should be borne in mind, 
however, that these areas are closely associated in their many 
activities, becoming increasingly so with the advance of 
relative intelligence. 

The center for vision is located in the occipital lobe; the 
visuo-sensory area is found in the cuneo-calcarine region, 
while the visuo-psychic area lies along the lateral aspect of the 
lobe (Figs. 66, 67 and 68). The optical radiation from the 
external geniculate body is rather extensive, but it appears 
to give a bilateral relationship about the calcarine fissure 
for impressions from the fovea centralis. 

The center for the sense of smell is believed to lie in the 
uncinate gyrus of the hippocampal lobe (Fig. 62). The 
evidence concerning the cortical location of the sense of 
taste is unsatisfactory, but such data as are at hand appear 
to indicate the location of this center in the hippocampal lobe 
just posterior and lateral to the cortical area for the sense 
of smell. 

The auditory center seems to be fairly well located in the 
superior temporal convolution both on its lateral aspect and 
on the area bordering the lateral fissure (Fig. 67). As 
with the optical radiation, it would seem that the auditory 
fibers are distributed to the cortex of both sides, though the 
main distribution is contralateral. 

There are four anterior prolongations of the cerebral 
cortex, the two lateral ones terminate anteriorly to form 
the retinse of the eyes, and the two mesial ones extend for- 
ward to form the olfactory lobes. 

The remaining portions of the cerebral cortex are largely 
given over to association activities; parts adjacent to definite 
centers are chiefly concerned with integrations of memories 
of correlated sensory impressions or impression groups. 


Thus, those areas proximate to the auditory area will be 
engaged in integrating and organizing memory impressions 
related to sound sensations, and should be especially well 
developed in musicians and philologists. Those areas adjacent 
to the cuneate lobe would serve as a repository for memories 
of visual integrations, and should be well developed in 
artists. Those in the upper parietal area adjacent to the 
bodily-sense convolutions would be concerned in the organi- 
zation of internal sense experiences, the conditioning of which 
may have much influence in determining the individual's 
moral standards. 

The frontal lobes seem relatively less important, though 
they are assumed to be involved in consummating the 
higher psychical processes; these parts show relatively the 
most atrophy in cases of dementia, and general paralysis 
of the insane; are the first to undergo dissolution in mental 
decadence; and are undeveloped in amentia; yet extensive 
unilateral disease of the frontal lobes may be present without 
producing notable symptoms— though ample comparative 
data on this point are lacking. A mentality that had 
never manifested any noticeable power of ratiocination might 
show but slight aberration even if the frontal lobes were 
beginning to atrophy. 

The cortex of the island of Reil is much more highly 
developed in man than in the lower animals, and the asso- 
ciation connections indicate a relationship with the higher 
areas. It would seem also to be related to both the motor 
and sensory sides of the speech area. 

The association areas of the cortex are generally regarded 
as ''the regions in which the different sense impressions are 
synthesized into complex perceptions or concepts" (Howell). 
And it would seem from all the evidence obtainable, histolog- 
ical, experimental, and pathological, that the efficiency of 
any area is primarily due to the anatomical endowment of 
that area (Fig. 69). If a specified area in one individual 
is more highly organized than the same area in another 
individual, then the one with the better equipment will, 
in that particular, have a higher potential intellectual 
capacity than will his less well-endowed brother. If we 



accept the fundamental doctrine of ''No psychosis without 
neurosis" then the more complete and intricate the histo- 
logical organization of any portion of the cortex, the more 
complex and efficient should be the functioning of that 
area. Mendelian experimentation indicates determinants 
of the most varied sort, affecting size, pigmentations, and 

^ '^^ 

Fig, 69. — A-D, Showing the phylogenetic development of mature nerve 
cells in a series of vertebrates: a-e, the ontogenetic development of growing 
cells in a typical mammal (in both cases only pyramidal cells from the cere- 
brum are shown); A, frog; B, lizard; C, rat; D, man; a, neuroblast without 
dendrites; h, commencing dendrites; c, dendrites further developed; d, first 
appearance of collateral branches; e, further development of collaterals and 
dendrites. (From Ramon y Cajal.) 

sundry other qualities; it may not be amiss to infer that like 
determinants exist in regard to the cortical structure and the 
sequential psychic potentialities. The pedagogical and 
sociological significance of a just recognition of this possi- 
bility is profound, and has not as yet been given due consid- 
eration. In a Mendelian sense a child may have deter- 
minants that permit its being an artist, but effectually 


prevent its ever being a mathematician; a boy may have a 
rich somesthetic endowment which will urgently need a 
social rather than a selfish expression. 

The infant comes into the world with a brain having the 
several lobes and convolutions characteristic of human devel- 
opment, though the associational complexity, and the 
intricacy of gyral development is greatly inferior to that of the 
adult. Reasoning from observations on animals, it is logical 
to suppose that the sensorium of the infant's brain possesses 
some traces of memories of all the great experiences through 
which the race has passed; such memory traces would con- 
stitute the physical basis of instinct. Surely if "ontogeny 
recapitulates phylogeny," then each system would be expected 
to evolve through its peculiar ontogenal groove, and thereby 
acquire those determinants characteristic of its inheritance. 
How much one can improve his inheritance is a debatable 
question, though all will probably admit an extensive adapt- 
ability to education of whatever may be the endowment 

The essential ground matter for mentality is sensation. 
A sensation may be defined as the first immediate awareness 
in consciousness of a molecular disturbance in the sensorium; 
the molecular disturbance is induced by a neural impulse 
conducted to the cortex by an afferent nerve from some sensi- 
tive area impressed by a stimulus. The sensation is thus a 
symbol in consciousness of the stimulus; it is referred by 
consciousness to the source of the stimulus; for example, a 
touch is referred to the area of cutaneous stimulation, or a 
sound is referred to an external source of vibration. 

According to the locus of reference, sensations may be 
classed as: (1) Exteroceptive, those in which the reference 
is to a source external to the body, as in touch, sight, or 
sound; (2) enteroceptive, those in which the reference is to 
a locus within the body, as in the vague visceral sensations; 
(3) proprioceptive, those in which the reference is to the 
somatic portion of the body, as muscle sensations. 

Qualitatively considered, the nature of the sensation 
aroused in consciousness depends on at least four factors: 


1. The physical nature of the stimulus, as when a steady 
pressure on the sole of the foot evokes an extensor response, 
but a painful pressure evokes a flexor response. 

2. Locus of incidence of the stimulus on the body, as when 
transverse waves of the ether falling on the retina produce a 
sensation of light, whereas if they fall on the skin they 
produce a sensation of warmth. 

3. Chemical nature of the stimulus, whereby one set of 
organs may be acted upon to the practical exclusion of any 
other, as in the sensation of taste. 

4. Central termination of the impulse. 
Quantitatively considered the sensation will vary, within 

narrow limits, directly with the strength of the stimulus. 
Some stimuli may be subliminal, thereby failing to induce 
a molecular agitation in the cortical cells; other stimuli may 
be so powerful as to rapidly fatigue either the peripheral 
sense area, or the recipient area in the brain. Through the 
phenomena of summation, a minimal stimulus becomes more 
effective by repetition, and a frequently-repeated subminimal 
stimulus may produce sufficient accumulation of energy as 
to break over the threshold and thus induce sensation. The 
quantitative effect may be modified by adaptation, as when 
the eye becomes accustomed to diminished light; or by con- 
trast, either tactile or visual. 

The amount of stimulation necessary to cross the limen 
is very small. Starling states that, in auditory stimuli, 
variations of air pressure amounting to less than 0.000,000,6 
mm. Hg., and having an amplitude of vibration less than 
0.000,000,7 mm., are adequate to induce a sensation of 
hearing; in terms of work, this variation amounts to about 
5.1 X 10=^^ ergs. Yet this minute variation evokes the 
sequence of mechanical effects through the external, middle 
and internal ears which, in turn, produce a neural discharge 
from the cochlear ganglia resulting in an auditory sensation. 

Physiologists assume that each sensation has a specific 
modality; that any single nerve fiber bears but one quality of 
sensation; that the character of the sensation, sound for 
example, is largely determined by the special sense organ; 
but the quality of the sensation, a harsh or sweet sound for 
example, is determined by the cortical termination. 


Simple sensations are not realizable as such in conscious- 
ness, inasmuch as the molecular disturbance in the sensorium 
must be somewhat diffuse; and the mind, on becoming aware 
of the molecular disturbance, immediately refers the disturb- 
ance to a real or assumed source, and such reference consti- 
tutes a compounded state in consciousness termed perception. 
But a single isolated percept is not realizable, inasmuch as the 
activity of any cortical cell must result in a series of neural 
discharges out over an indefinite number of association paths 
awakening an ever-widening number of perceptual memories, 
any or all of which may enter into the formation of a judg- 
ment concerning the original percept. For example, together 
with the sensation aroused on perceiving a point of light, are 
kindred sensations and percept memories involved in deter- 
mining the luminosity of the point, its color, position, and 
the distance from the observer, and the possible significance 
of the light. 

From the physiological outlook all knowledge is perceptual 
in origin, either by acquirement or by inheritance. Knowl- 
edge of the qualities of any object is obtained through the 
senses; and though such knowledge may become generalized, 
yet its essence is perceptual. No amount of ratiocination 
can deduce the actuality of an object; its qualities as revealed 
by perception represent the limit of the ascertainable. 
Infants, like animals of unifocal vision, have percepts in one 
plane only; later, when other sensations give modifying per- 
cepts, the resulting mental state becomes materially altered. 
Thus it is that early percepts in the young, like novel per- 
cepts in adults, may readily yield inaccurate information 
to consciousness; sensations may be incorrectly referred, 
perceptions may be inadequately estimated; only as there is 
acquired by experience a vast number of percepts does the 
mental picture approximate reality. Especially may error 
arise if the object perceived be an unfamiliar one, or one 
perceived while in an unusual position or when observed 
from an unaccustomed angle ; or, again, a faint sensation may 
be translated into an erroneous perception. 

A perception will vary according to the intensity of 
the sensory impression. What might result from subliminal 


sensations— those too weak to become apprised to conscious- 
ness—is purely speculative, though the summation of such 
stimuli might eventuate in a definite percept. Any stimulus 
which crosses the threshold of consciousness will evoke that 
perception whose associative attributes are at that moment 
most dominant; strong stimuli will establish very definite 
and persistent percepts and mental states. 

Since perceptions are the reference of sensations by 
consciousness, the possibilities for error are many. When 
the error is in the reference, the sensation being normal, the 
resultant in consciousness is termed an illusion. There are 
illusions of touch, of the muscle sense, of hearing, and a great 
number of illusions of sight; most of these illusions arise from 
perceiving a known object in an unaccustomed or unusual 
relation. When the error arises from an abnormal sensation, 
as for example, when the reference is evoked by some intrin- 
sic molecular disturbance not immediately dependent on a 
sensory stimulus but arising rather from some aberrancy of 
metabolism— such an error is termed an hallucination. 
Hallucinations assert an objective reality where none exists. 
Assumedly the reference of the perceptive faculty is correct, 
but there is a subconscious misinterpretation. Certain 
cortical cells are surely transmitting definite impulses; and 
messages from this area, having had hitherto a specific 
meaning, continue to be interpreted by consciousness in the 
accustomed manner. To the mind there must be an objective 
reality for the sensation experienced, for is it not producing a 
perturbation in consciousness? 

These localized and abnormal molecular disturbances 
producing hallucinations may be provoked by several means, 
but some interference with normal mental continuity is 
essential. Such mental disturbance may be the result of 
partially suspended consciousness, as in day-dreams, or it 
may be due to drugs, or to poisons, or to a shock, or to disease. 
With consciousness thus disturbed, a vivid impression in 
memory, or even some fancy, may repeat itself with marvel- 
ous fidelity of detail. Both illusions and hallucinations 
are readily provoked by suggestion; in this condition, con- 
sciousness is more or less in abeyance, while memory and 


imagination are free to supply the necessary stimuli to the 
perceptive faculty. Certain drugs, like alcohol, opium, and 
hashish, provoke molecular excitements resulting in very 
pronounced hallucinations. High fevers are sometimes 
accompanied by such disturbances; insanities almost invari- 
ably are. 

These considerations concerning hallucinations might 
lead one to speculate on the possibility of autogenous molec- 
ular vibrations in brain cells as a result of normal cellular 
metabolism, or as affected by variations in the composition 
of the blood stream. Concerning the former of these two 
suppositions nothing conclusive may be adduced; of the latter, 
we have very definite evidences of the effects on consciousness 
of diminished blood volume, of the effects of exogenous poi- 
sons, and not a little presumptive evidence of the effect 
of endogenous toxins; but the whole subject needs further 
extended investigation. 


Piper: Velocity of Nerve Impulse in Man, Pfluger's Archives, 1909, 127, 

Kramer: Function of Spinal Ganglia, Jour. Exp. Med., 1907, 9, 314. 

Schafer: Spinal Paths for Volitional Impulses, Quart. Jour. Exp. Phys., 
1910, 3, 355. 

Black: Cerebellar Localization, Jour. Lab. Clin. Med., 1916, 1, 467. 

McDougall: Frontal Lobes as Seat of Psychophysical Processes, Brain, 

Leyton and Sherrington: Motor Areas in the Higher Apes, Quart. Jour. 
Exp. Phys., 1917, 11, 135. 

Anderson: Autonomic Nervous System, Jour. Phys., 1902, 28, 499. 

Herrick: Neurology, 1922. 

Tilney and Riley: Functions of the Nervous System, 1921. 

Ransom: Anatomy of the Nervous System, 1920. 

Bush: Accountability, Quart. Jour. Univ. North Dakota, April, 1921. 

Gaskell, W. H.: The Involuntary Nervous System, 1916. 

Head, H.: Studies in Neurology, 1920. 

Sherrington, C. S.:. The Integrative Action of the Nervous System. 

Herrick, C. J.: Neurological Foundations of Animal Behavior, 1924. 



Were it not so commonplace as to be calmly accepted 
without much comment, the fact that everybody normally 
lapses into unconsciousness each night would be regarded 
as one of the most remarkable of phenomena; for not only 
does a person experience this loss of consciousness daily, but 
he thereby spends about one-third of his existence in a coma- 
toid state. Underlying this phenomenon of sleep, there must 
be some great elemental need; yet what may be the real 
nature of this need remains a mystery. Several more or 
less plausible theories have been advanced in an attempt 
to explain the mystery. 

Theory 1. Accumulation of Acid Waste Products.— It is known 
that all muscle activity is accompanied by the release of an 
acid product. For the most part this acid product is promptly 
eliminated from the body, through the lungs as carbon 
dioxide, or as an acid salt in the urine. However, it is 
thought that a residuum may accumulate, during the period 
of major activity; and that for its elimination a period of 
comparative quiescence is essential, to the end that adequate 
opportunity may be afforded the body for getting rid of 
accumulated katabolites. 

This theory finds not a little support in the following 
experiment. If, from the blood of a dog just in from a 
long exhausting chase, some serum be taken and injected 
into the blood stream of a fresh dog, this second dog will 
promptly manifest the several symptoms of approaching 
exhaustion, including sleep. Or even if lactic acid be in- 
jected into the lymph spaces of a fresh dog, there will soon 
ensue the symptoms of great fatigue, even unconsciousness. 


Theory 2. Accumulation of Sleep-producing Toxins.— This 

theory is conceived somewhat more vaguely; it assumes that 
various toxins of katabolism accumulate in the body as a 
normal sequence of activity, and these toxins finally pro- 
duce such an obtunding of the brain cells as to induce the 
unconsciousness that insures sufficient quietude for gradual 

Theory 3. Anemia of the Brain.— Sleep seems to be accom- 
panied by a diminished amount of blood to the brain, but 
whether this condition induces sleep or is simply a natural 
concomitant is not certain. Increased cerebral activity 
causes a definite determination of blood to the brain; dimin- 
ished mental activity would probably be accompanied by a 
reverse determination. Then, too, increase of the flow of 
blood through the brain, as may be induced by moderate 
doses of caffein, temporarily heightens intellectual activity; 
while a rapid lowering of the cerebral blood supply, as in 
attacks of fainting, usually is quickly succeeded by uncon- 
sciousness. From such data, in part, Howell has developed 

Theory 4. Fatigue of the Vasomotor Center.— This theory 
assumes that the medullary center which controls the caliber 
of bloodvessels throughout the body becomes tired as a 
result of its constant activity during the day, and gradually 
declines in tone; as a result, the normal constrictor impulses 
sent therefrom gradually diminish in force, the systemic 
bloodvessels slowly dilate, and anemia of the brain ensues 
mechanically, with unconsciousness as an inevitable sequence. 

It seems more probable to assume that each factor urged 
in the separate theories has a substantial, though not exclusive 
basis. Very probably there is a slow but steady accumulation 
of toxic waste products, and these, demonstrably, have a 
soporific effect on the brain; any additional influence tending 
to induce an approximate anemia will aid also in bringing on 
a state of unconsciousness. But whatever may be the 
factors involved in producing sleep, the period of quietude 
undoubtedly serves as an occasion and opportunity wherein 
anabolism may overtake katabolism; therefore, sleep is a 
period of recuperation. Without sufficient sleep the stresses 
of existence rapidly exhaust the reserve forces; but, with 


adequate sleep, the reserves are so well maintained as to 
serve efficiently in many an hour of need. 

Intensity of Sleep.— The intensity of sleep has been meas- 
ured by noting how loud a sound was required at different 
hours of sleep to awaken the sleeper. As shown by the 
clinical curves, one sleeps most soundly during the first 
hour or two after unconsciousness comes on, then much 
more lightly during the balance of the recuperative period. 
Children usually show a second augmentation of the depth 
of slumber at about the sixth hour. 


Consciousness may, tentatively, be defined as the aware- 
ness of a continuous in-and-out streaming of sensations 
and perceptions, simple or compounded, or of the more or less 
integrated memories of those fundaments. It is doubtful 
if consciousness is ever completely suspended throughout 
life. The modality of consciousness is varying constantly; 
its awareness efficiency reaches a maximum normally in the 
earlier hours of waking, and falls to its customary minimum 
during the first hours of sleeping. In the later hours of 
sleeping, the level of consciousness is but slightly below the 
norm of the waking hours; in fact, during this period, con- 
sciousness is more or less feebly aware of the stream of sen- 
sations and the intermingling intellectual flotsam. When 
consciousness is at its point of maximum efficiency, it seems 
able to follow, with varying success, any given concept or 
percept drifting into attention; but when consciousness is 
below an average mean, or is below the waking limen, its 
power of awareness does not seem to be yoked with any 
power of fixation; in this latter condition, consciousness 
idly views, as it were, the mass of phantasmagoria drifting 
chimerically by. 

The content of these phantasmagoria consists always of 
memories of past experiences, ideas, or associations, seem- 
ingly absurdly intermingled and juxtaposed, and more or less 
modified at the present moment by the sensations constantly 
drifting in from the entire periphery— both of the autonomic 


and systemic distributions. The autonomic afferents seem 
relatively less resistant to the passage of sensations on 
cephalward during sleep than when consciousness is above 
the waking threshold; though even now, the autonomic 
afferents act chiefly to initiate their normal reflex responses, 
and it is the secondary reactions that induce the somatic 
sensations dimly apprehensible in consciousness. 

The sequential order in dreams seemingly is frequently 
illogical; this is because consciousness fails itself to link 
up in logical order the leading appearances with their cognate 
associations. The dream associations are perfectly logical, 
from a mechanical standpoint; always the linking up of a 
given percept with some cognate percept, even if the perti- 
nency of association and correlation is not manifest to the 

The content of dreams may be drawn from any of the 
experiences, real or imagined, in the life of the individual. 
Many of the phenomena of mnemonics indicate that all one 
sees, hears, or experiences in any way, awake or asleep, 
immediately or remotely, becomes thenceforth an integral 
part of the mental life. Seemingly this immense repository 
may be tapped at any point during the dream state, the 
hypnoidal state, and frequently during the waking state ; and 
the combinations ensuing therefrom and thenceforth may be 
quite strange, bizarre, and fantastic. 

It is conceivable, even probable, that racial experiences 
may modify dream states to some extent. All the emotions 
are phylogenous; many of the dominating activities of the 
mind at peace, and most of them of a mind enraged, are of 
origin far antedating the life of the individual; and as all 
activities have emotional correlatives in the waking state, 
so must they be similarly correlated in the dream state. 

So, all dreams may be considered but hollow reechoes 
from the past; they can have no prophetic significance 
whatever— except, indeed, as they may faintly indicate the 
way of inexorable destiny. Undoubtedly there have been 
some remarkable resemblances between a present dream and 
a future outcome, but these are merely coincidences; the 
number of such reported cases is far less than we might 


reasonably predicate from the law of probabilities. To 
assume that an event yet of the future can possibly be woven 
into a dream of the present is to wilfully ignore the necessity 
of antecedent causality. 

In the various hypnoidal states there are partial sus- 
pensions of normal consciousness; whatever consciousness 
may continue, its awareness seemingly becomes highly sen- 
sitized to a few sensory avenues, all others being temporarily 
in more or less abeyance. In the hypnoidal state the flow 
of the stream entering consciousness seems partially directa- 
ble; possibly, though as a matter of relative inhibition of the 
present seemingly nonessential. In this state the subject 
awaits suggestion as if at that moment he were just entering 
or leaving the maximal dream state; without being truly 
asleep, he is so mentally, for the nonce. Consequently, 
all the storehouse of subconsciousness lies there open before 
him, though usually neither operator nor subject seems 
capable of utilizing therefrom more than the merest modicum. 
Yet the subject's paraphernalia for dreaming seem sensitive 
to the capricious suggestion of the operator, so that what- 
ever the operator may suggest becomes easily (though not 
inevitably) the dream substance of the subject. It is 
interesting to note, however, that though the dream may have 
its inception from the suggestion of the operator, the progress 
of the dream will be largely determined by the subject's 
habits of life and customs of thought; a repugnant suggestion 
will not be accepted. Whatever the eventuating hypnoidal 
dream state, the events therein will be sequentially logical. 


Trance states may be considered temporary, and more or 
less complete, disassociations of a consciousness in which there 
seem to coexist two personalities, a normal dominant one 
and an abnormal recedent one. In such a state, the normal 
dominant consciousness becomes temporarily recedent— 
subconscious, as it were— while the abnormal recedent 
personality, the ''control", becomes ascendant for the time. 
Careful investigations seem to indicate that this other 


consciousness, the "control" of the medium, has no further 
informational source than has the waking consciousness, 
though its store of information may be more readily appre- 
hensible. Just as the hypnotized subject, in partial sub- 
mergence of the waking consciousness, can sometimes tap 
the wellspring of the subconscious, so probably can its 
analog, the "control", or disassociated consciousness. Hence 
the occasional appearance of those remarkable recitals 
concerning which the auditors know nothing, and about 
which the dominant consciousness will disclaim all knowl- 
edge. Yet in the very nature of things, the "control" is 
able to resurrect material out of the past only, material 
which may have escaped the waking consciousness utterly, 
yet material which has been stored fatally, even though its 
resurrection by the mind is possible only when the heavy 
inhibition of the normal waking consciousness has been 
suspended. The many points of resemblance between the 
trance state and the hypnoidal state is suggestive of a close 
causal relationship; and neither is far removed from the 
normal dream state. 


Emotions may be considered to be highly-integrated 
phylogenetic memories. They represent the tenuously- 
sublimated inheritance-memories of the multitudinous sen- 
sory-motor reactions through which the race has passed in 
its long struggle for existence and perpetuity. Any emotion 
that may be mentioned has its evolutionary analog in some 
systemic reaction or series of reactions common to evolution- 
ary development. The antiquity of the origin of emotions 
is indicated by the intimacy of association each bears with 
the autonomic system. Long before reason had learned to 
modify emotional response, the reflexes conducing to indi- 
vidual or racial well-being and continuity had become 
firmly established. 

All the emotions are definable in terms of reflex response 
to physical needs; the feeling which we now define as an 
emotion is concurrent with the response. Professor James 
inverted the common idea that one laughs because he is happy 


into the seemingly paradoxical idea that one is happy because 
he laughs. It may be more nearly correct to say that the 
facial contractions accompanying laughter are but funda- 
mentally reflexes developed originally from sundry sensory 
stimuli; while the accompanying mental state, the emotion, 
is but incidental and concurrent— something added on as the 
reflex develops. 

For example, consider the emotion of fear. Genetically 
this emotion originated from a multitude of memories 
connected with flight, or correlated with combat, or associated 
with suffering. Ultimately the multiplicity of memories 
would become fused into a fairly definite memory-concept 
closely coordinated in its neural connections with those 
autonomics having to do with protopathic responses. So, 
when danger threatened, the memory-concept instantane- 
ously induced the essential autonomic reaction; this is 
simply a compounded sensory-motor reflex. The eventuating 
of this reflex is apprehended in consciousness as the process 
proceeds, and that apprehension of the reflex is spoken of 
as the emotion of fear; but the apprehension itself is in essence 
the memory of a memory-complex. 

In his Mental Evolution in Animals, Romanes shows that 
emotional responses may be observed far down the animal 
scale. The earlier emotions are concerned mostly with those 
muscle reactions having to do with individual safety; later, 
are those correlated with group relationships. The simply 
egoistic persist tenaciously, with but slow yielding to the 
altruistic ; very few are the emotions untinctured by primitive 
neuro-muscular reactions. 



Some of the sensations entering consciousness have 
aheady been discussed, especially the tactile sense, muscular 
sensibility, and the senses of pain and temperature. But 
there are several other avenues through which information 
reaches consciousness, concerning either the condition of the 
body or its environment. These may be grouped as follows : 
Enteroceptive, those of hunger and thirst; Proprioceptive, 
those of the muscles and joints; Exteroceptive, those of seeing 
and hearing, touch, 'taste and smell. 


The sensation of hunger is a vague though imperative 
condition of the body. Its immediate cause consists of 
variations in the muscular condition of the cardiac portion of 
the stomach; but more fundamental to these there is a 
systemic need which expresses itself in hemic modifications. 
Some writers. Cannon for instance, seem inclined to locate 
the hunger sense solely in the stomach; they adduce exten- 
sive experimental data proving that hunger accompanies 
definite contractions of the gastric musculature; and it 
would appear to have been conclusively shown that these 
contractions produce the sensations registered in conscious- 
ness as hunger. Yet provocative of these hunger contractions 
exists an obscure bodily need which makes itself known 
through some variation in the blood stream whereby the 
hunger contractions are stimulated; but whatever this may 
be, it seems to lose early its full force inasmuch as hunger 
pangs usually diminish in a few days and finally disappear 
altogether— at least such is the testimony of professional 


The contractions in the stomach producing the sensation 
of hunger are different in quahty from those accompanying 
peristalsis. This is shown by the fact that hunger pangs 
cease as soon as food enters the stomach and the normal 
processes of digestion begin, although the peristaltic waves 
are henceforth more active. Hunger contractions persist 
after severance of the vagi and sympathetic nerves, showing 
that the intrinsic ganglia of the stomach are the effective 
neural apparatus; the activity of these ganglia seems to be 
heightened by vagal stimulation, and inhibited by splanchnic 
influence; an inhibitory effect is produced also by either 
mechanical or chemical stimulation of the mucous membrane 
of the mouth, esophagus, or stomach. 

The utility of the hunger sense consists in the normal ''reg- 
ulation of the amount and quality of food necessary to. the 
proper nutrition of the body." Opposite to the impelling 
sense of hunger is the feeling of satiety which, by overeating, 
may amount to aversion— a sensation quite the opposite 
in quality to the sensation accompanying the feeling of hun- 
ger. A further indication of the part played by metabolism 
on the hunger sense is shown by the fact that after feeding 
for a short while on gelatin, an animal will starve before 
partaking of any more of the same substance. 

Appetite.— A distinction is made between appetite and 
hunger. Appetite is a pleasurable mental state aroused 
in part by sensations from the stomach, but principally 
from sensations arising from the organs of taste and smell, 
together with memory associations of related stimuli; 
hunger, on the other hand, is a more or less disagreeable 
sensation located approximately in the musculature of the 


The sense of thirst depends fundamentally on the relative 
water equilibrium of the bodily tissues. Considerable 
quantities of water are lost daily through the lungs, skin, 
and kidneys; and though the blood probably maintains its 
specific gravity approximately normal through water abstrac- 
tion from the tissues, yet it may be that slight variations 


ill the water balance of the blood are sufficient to effect 
variations in the pharygeal mucosa; this seems to be indicated 
by the sensation of faucial dryness which soon follows tem- 
porary but brief deprivations of water. A further indication 
that the mucosa of the pharynx serves as a special end- 
organ of thirst is shown by the way small amounts of water 
relieve such sensations of dryness as are induced by a dry 
and dusty air, or by dry and salty food. 

Whenever there is a prolonged deprivation of water, 
there is associated with the sense of thirst, a feeling of 
anguish and deep distress; this is probably due to metabolic 
impressions from many areas. 


The sense of taste is so intimately associated in the lay 
mind with the sensations arising from olfactory stimuli as to 
be very imperfectly delimited. Gastronomic epicureans who 
pride themselves on their highly-discriminative gustatory 
sense would probably be greatly surprised to learn it was 
the sense of smell rather than that of taste they had culti- 
vated so assiduously. As a matter of fact, there are but 
six varieties of the sense of taste : Sweet, acid or sour, bitter, 
salty, alkaline, and metallic; but there are, of course, a great 
number of blended tastes produced by the simultaneous 
or immediately successive stimulation of two or more taste 
areas by sundry mixtures of the several stimuli. Also, 
mingled with the specific taste sensations are sensations of 
common sensibility, produced by many acrid, pungent, or 
otherwise irritating substances. 

The sense of taste is located chiefly on the tongue though 
possibly existing to a limited extent also in the soft palate 
and epiglottis. The taste sense is not distributed uniformly 
over the tongue, but is most marked at the tip, sides, and 
posterior third of the dorsum. The sense of sweetness is 
most apparent at the tip of the tongue; sourness, along the 
sides; and bitterness, in the environs of the circum vallate 

If different sensations are aroused simultaneously there 


results a modification of each. If the stimulation is weak, 
one sensation may annul the other, as for example, a salt 
solution renders a weak vinegar solution almost tasteless. 
The combination of two tastes may be a pleasant resultant 
in consciousness, even though the two components are readily 
distinguishable, as from the well-known lemonade beverage. 
In another case, the sensibility for one case may be heightened 
by the previous stimulation of another, as salt added to 
distilled water produces a vague sensation of sweetness. 
Sweet sensations are accentuated if the stimulus is cool, 
but acid sensations are accentuated when the stimulus is 
hot. The threshold of taste varies greatly with different 
individuals, but with the majority the sensation for bitter is 
most marked. 

The end-organs for the sense of taste are represented by 
oval bodies located in the stratified epithelium of the tongue. 
The fusiform cells forming the end-organs have delicate 
processes projecting out to the surface of the tongue; these 
processes are the part first affected by sapid substances. 
The end-organs are not affected by any substance not in 
solution or capable of being somewhat dissolved by the saliva; 
it is assumed that a chemical reaction takes place between 
the protoplasm of the end-organ and the sapid substance, 
and that the quality of the taste sensation depends somehow 
on the chemical constitution of the substance tasted. Yet 
we know little as to how this may be, or why such dissimilar 
substances as sugar, saccharin, and acetate of lead should 
each arouse a sensation of sweetness, while soluble starch, 
which is so closely related to sugar, produces practically no 
sensation of taste whatever. 


The sense of smell in man is apparently rudimentary 
or vestigial. In primitive times it was probably of great 
value in determining the location and quality of food, and 
might be utilized wisely for this latter purpose in these days. 
It is one of the oldest of sensations phylogenetically; and its 
information to consciousness is usually very marked and 


definite as regards relative pleasantness. Its present phy- 
siological utility is in relation to appetite. 

The end-organs for the sense of smell are located in the 
upper nasal chambers. They are acted upon by gaseous 
particles floating in the atmosphere; these are brought 
into contact with the mucosa of the olfactory region through 
inspiration air currents. The ability to discriminate between 
odors, the fact that some individuals perceive certain odors 
but not others, the rapidity with which the olfactory appara- 
tus becomes fatigued for some odors while remaining excitable 
to others, all these facts indicate that in the olfactory appa- 
ratus there are specific responses, and that there are definite 
qualities for each of the sundry odors. 

Odors are usually classified according to the relative 
agreeableness of the sensations produced, a grouping which 
rests largely on individual prejudice and opinion. Besides 
the pure odors, or odors proper, there are many which are 
mixed with common sensibility stimuli from the nasal mucosa, 
as well as those which are mixed with the sense of taste. 
Many odors are intimately associated with personal experi- 
ences, especially those connected with the sense of taste; 
and many are associated with social experiences. The 
extent to which flavors are used in foods and beverages, 
and the commonness of the use of perfumery indicate some 
deeply-seated correlation between the olfactory stimuli and 
other somsesthetic reactions. 

Limits of the Sense of Smell.— The amount of odoriferous 
particles required for exciting the sense of smell is extremely 
small. For example, 0.01 mg. mercaptan, placed in a room 
6 meters high and square, is distinctly perceptible in any part 
of the room. In this case, in each inspiration the total 
amount of mercaptan available to affect the olfactory area 
would be less than 0.000,000,02 mg. 


Auditory sensations are those which are aroused by 
means of longitudinal vibrations of air impinging on the audi- 
tory apparatus. The physical nature of such vibrations has 
been reviewed in the course in Physics^ so it will be unneces- 
sary to refer to those phenomena except to illustrate sundry 

Vibrations of air from any source of sound pass through 
the external auditory canal to the tympanic membrane. The 
functions of the external ear in collecting and accentuating 
the volume of air waves is very small, especially in comparison 
with the movable, cone-shaped ears of many of the lower 
mammalia. Movability of the ear was probably a condition 
possessed by primitive man, or his prototypes, as indicated 
by the vestigial muscles of the ear; these muscles assumedly 
had at one time the function of altering the plane and posi- 
tion of the pinna, as well as deepening the cavity of the 
concha. The present contour of the concha is such that it 
may to some extent modify the direction and square-area 
intensity of sound waves. 

The curve and depth (about 2 cm.) of the external auditory 
canal, together with the presence near the orifice of hair and 
a secretion of "wax," indicate that the immediate receiving 
mechanism, the drum, is deeply placed for protection against 
possible violence as well as to be shielded from drafts and 
marked changes of temperature. 

The tympanic membrane is curiously constructed. Though 
but 0.1 mm. in thickness, it consists of three layers; an outer 
layer of epithelium, a middle fibrous layer of both radial 
and concentric groups, and an inner layer of modified mucous 
membrane. In shape it is a very shallow conical disc, 



placed obliquely so that its outer face looks outward, down- 
ward and slightly forward; Cunningham also states that the 
ear drum is least obliquely placed in musicians, and most 
obliquely in cretins and deaf mutes. Apparently this mem- 
brane responds to every delicate variation of vibration, 
whether in volume or frequency; and its peculiar structure, 
together with the damping effect of the attachment of the 

Fig. 70. — Chain of ossicles and their ligaments, seen from the front in a 
vertical, transverse section of the tympanum. (Testut.) 

handle of the malleus, effectually prevents its having any 
vibration periodicity of its own, otherwise the membrane 
would tend to emphasize such particular tones and overtones 
as accorded with its own period. 

The inner surface of the tympanic membrane has attached 
to its vertical radius the handle of the malleus (Fig. 70). 
Any movement of the drum then results in a swing of the 
malleus on its particular axis. This axis of rotation of the 


malleus is nearly horizontal, and lies at about the same level 
as the superior border of the drum, at which point is a process 
by means of which the malleus is attached to the tympanic 
cavity, while above is the rounded head for articulation 
with the incus ; and as the incus is so suspended by a ligament 
as to give it a balanced lever action, any movement inward 
of the handle of the malleus causes a similar movement inward 
of the long inferior process of the incus. To the lower extrem- 
ity of the inferior process of the incus is attached the head 
of the stapes; and, as the foot of the stapes is attached to the 
membrane covering the foramen ovale, any movement of the 
drum produces a coordinated movement of the oval mem- 
brane in the same direction. But though the oval membrane 
moves synchronously with the tympanic membrane, yet 
its amplitude of action is but two-thirds as much; this is due 
to the fact that the length of the malleus to the long process 
of the incus is as 3 to 2, whence it follows by the laws of levers 
that while the amplitude of movement is diminished in the 
ration of 3 to 2, the force of action is increased in the ratio 
of 2 to 3; and as the area of the memhrana ovale is but one- 
twentieth of the tympanic membrane, the pressure on the 
oval membrane must be increased thirty fold over that of the 
tympanic membrane. 

It has been possible to observe with a microscope the actual 
movements of the malleus when* sound waves are falling on 
the tympanic membrane. When so observed, the maximum 
movements of the tip of the malleus at the apex of the drum 
were about 0.04 mm., though sounds seemed plainly audible 
when the movements were so slight as to be imperceptible. 
In fact it has been stated (Starling) that a musical tone having 
an amplitude of vibration equivalent to 0.000,000,006 mm. 
can be easily heard; this indicates how extremely sensitive 
must be the apparatus w^hich can pick up such minute varia- 
tions in air pressures. 

The tympanic cavity (Fig. 70) is a very irregularly-shaped 
cavity having no probable resonance period of its own. 
Through the Eustachian tube it communicates w^ith the 
throat and hence with atmospheric pressure; and though 
the Eustachian tube is normally closed, it seems to open 




whenever the pharyngeal muscles contract in the act of 
swallowing, thus permitting the maintenance within the 
cavity of an equilibrium of air pressure. Any occulusion of 
this tube, such as not infrequently occurs with nasal ''colds/' 
promptly results in a rarefaction of the air in the tympanic 
cavity and interference with the freedom of the vibrations 
of the tympanic membrane. 



Lamina spiralis 

. ■ o&sea 

Ty7nj?amc cavity 


Scala vestibuli 
Scala tympani 

Vestibular fenestra 
Fissura vestibuli 

Fossa cochlearis 

Lat. semicircular 


Post, semicircular 


Reces suscepticus 

Fig. 71.^ — The cochlea and vestibule, viewed from above. All the hard 
parts which form the roof of the internal ear have been removed with the 
saw. (Gray.) 

Within the tympanum are two muscles, the tensor tympani 
and the stapedius. Contraction of the tensor tympani draws 
the handle of the malleus mesalward, and in that way increases 
the relative tension of the tympanic membrane. Hensen 
contends that this muscle contracts reflexly to all acoustic 
stimuli; and it would also seem that this muscle can be vol- 



untarily contracted when attention is trained acutely on a 
possible apprehension of some seemingly indistinct sound. 
The stapedius muscle serves to tilt the base of the stapes, 
and draw it slightly outward; thereby rendering more tense 
the stapedial membrane, and thus heightening auditory 

The vibrations of the ossicles, initiated by movements of 
the tympanic membrane, are transferred to the structures of 
the inner ear through the oval membrane. Mesally this 

Fig. 72. — Diagrammatic longitudinal section of the cochlea. (Gray.) 

membrane is in contact with the perilymph of the scala 
vestibuli (Figs. 71 and 72), so that the vibrations from the 
middle ear are repeated in the incompressible fluid of the 
perilymph; provision is made for these surging movements 
by a continuation of the scala vestibuli through the helico- 
trema (Fig. 71) into the scala tympani at the distal end of 
which is a flexible menbrane, the membrana rotundum. 

Referring to the anatomy of the internal ear (Figs. 72, 
74 and 75), it will be observed that the cochlea, which part 



of the internal ear alone is concerned with auditory impres- 
sions, has its spiral canal subdivided into three sections, viz. : 
A central one the scala media, (or ducutus cochlearis), sepa- 
rated from the scala vestihuli by the membrane of Reissner, 
and from the scala tympani by the basilar membrane. The 
scala media is practically a closed membranous sac, filled 

Connective tissue binding 
duct to periosteum 

Semicircular duct 

Fibrous band uniting 
free surface of duct 
to periosteum 



Fig. 73. — Transverse section of a human semicircular canal and duct. 
(After Rlidinger.) 

with the endolymph, and lying loosely suspended in the 
perilymph. Any vibrations of the perilymph are readily 
transferred to the endolymph, through the membrane of 
Reissner, and the vibrations of the endolymph agitate the 
structures acting as end-organs for the auditory nerves. 

The terminations of the auditory nerve filaments are 
within a peculiar modification of the scala media termed the 



organ of Corti (Figs. 72, 76 and 77). The essential portions 
of the organ of Corti are: (1) the basilar membrane; (2) 

Recessus ellipticus 


Orifice of aqucediictus vestibvli 

„ 7 7 • ' / Orifice of aquceductus cochleae 

Fossa cochleans / ^ j -i 

Cochlear fenestra 
Fig. 74. — Interior of right osseous labyrinth. (Gray.) 


Fig. 75. — The membranous labyrinth. (Enlarged.) (Gray.) 




the rods of Corti; (3) the cells of Deiters; (4) the inner and 
outer hair cells. These last structures, the hair cells, are 
the true end-organs of hearing, as indicated by the fact that 
to them pass the filaments of the auditory nerve; these fila- 
ments break up into minute terminal brushes about the nuclei 

■ Menibrana basilaris. 
Canal of 

Fig. 76. — Floor of ductus cochlearis. (Gray.) 

Membrana tectoria. 


Cells of Deiters. —'«--«- 

Outer rod- 
Nerve fibres. 

Basilar membrane. 

Fig. 77. — Section through the organ of Corti. Magnified, (A. Retzius.) 

of the hair cells (Fig. 77). Therefore there is justification 
for the conclusion that whatever may be the intermediate 
processes whereby vibrations of the endolymph are trans- 
mitted to these cells, the hair cells are the true end-organs. 
Several theories have been advanced to explain how the 
multitudinous variety of sounds could be selected by the 


appropriate hair cells in the organ of Corti, and the specific 
stimulus sent thence to the brain. Helmholtz's original 
theory was that the rods of Corti were resonators that 
responded to specific vibrations. But the excess of hair 
cells over rods makes this theory seem improbable. (It 
is estimated by Retzius that there are about 3850 outer rods 
and 5600 inner ones; while there are about 3500 inner hair 
cells and about 18,000 outer ones.) Then at Hensen's 
suggestion, Helmholtz proposed that the basilar membrane 
might be the resonating apparatus. This membrane 
increases in width steadily from 135 microns in the basal 
portion to 234 microns at the apex, thus giving it a harp-like 
arrangement of its longitudinal fibers; now, if it be assumed 
each fiber has a specific vibration period of its own, it would 
seem that the hypothesis were a plausible one. It is further 
assumed in this theory that the vibrations of the fibers are 
communicated to the rods of Corti and thence in some way 
to the hair cells. But this theory has not been generally 
accepted. First it involves a transmission of the vibrations 
either through the helicotrema, or through the endolymph and 
the organ of Corti to the basilar membrane; second, it 
assumes that the 24,000 strings in the basilar membrane, 
each of which is inevitably more or less damped by the 
epithelial tissue below and the cells above, shall transmit 
specific vibrations through 9000 rods of Corti to affect with 
delicate distinction some 20,000 hair cells. 

A simpler theory is that of Ayers which, while it has not 
yet had adequate histological confirmation, has the merit of 
greater plausibility. Overhanging the hair cells is what in 
histological preparations appears to be a hair-like membrane 
termed the tectorial membrane (Fig. 76). In other theories 
this membrane is thought to be a damping mechanism for 
stopping the vibrations of the hairs when these are once 
started, though it would seem that such contacts would be 
more likely to initiate a stimulus than to check one. So 
Ayers assumes that, in the natural condition, the tectorial 
membrane consists of a fringe of delicate hairs of constantly 
increasing length from the base to the apex; that these hairs 
are loose in the endolymph overhanging the hair cells; and 


that perilymph vibrations, passing readily through the deli- 
cate membrane of Retzius, throws the endolymph into 
isodynamic vibrations, and that those tectorial hairs only 
that have the same vibration period respond with a vertical 
swing which brings them into contact with the hairs of the 
hair cells, thereby initiating a neural impulse in the nuclei 
of the hair cells. Naturally when the tectorial hairs do not 
touch the hairs of the hair cells, no stimulation occurs; 
hence no provision for a damping mechanism is needed. 
This theory admits of an explanation of practically all the 
phenomena of physiological sound; the chief objection raised 
against it is that it has not been proven histologically. 

It may not be amiss to add that we accept the fact that 
certain transverse waves affect the hot spots on the skin 
but not the cold spots, yet no histological differentiation is 
ascertainable; that certain other transverse waves affect 
certain rods and cones in the retina but not other retinal 
cells; that some taste buds are stimulated by sweet stimuli 
but not by sour; that certain olfactory end-organs respond 
to balsamic odors, and others to fetid odors; so one is not 
accepting anything more qualitatively if he assumes that the 
hairs of certain hair cells respond to a specific vibration 
frequency of the endolymph but to no other. To be sure 
this also assumes a remarkable complexity of mechanical 
sensitivity, but such a marvel the organ of Corti is anatomic- 
ally, and may well be physiologically. Of course, such a 
theory of audition leaves for future explanation the problem 
of the actual mechanics involved. 

A so-called telephone theory has been advanced whereby 
the entire organ of Corti is assumed to vibrate like the metal 
plate in a telephone receiver, leaving to the cortex the 
function of discriminative selection. This theory seems 
to ignore the wonderful anatomical mechanism of the organ 
of Corti with its seeming potentiality for selective adaptation; 
hence it does not seem to merit extended consideration. 

Assuming that the end-organ constitutes the selective 
mechanism, there is here involved a complicated power of 
discrimination. Analysis is made of the amplitude and pitch 
of simple sound waves, and of the several constituents and 


qualities of compound tones. The physical antecedents of 
these several factors indicate to some extent the modus 
operandi of this discrimination. The amplitude of vibra- 
tion of a sounding body, it will be recalled, is what determines 
its relative loudness to the ear, while its rapidity of vibration 
is what determines its pitch. We can easily conceive that 
relative amplitude of air vibration is transmitted with exact- 
ness by the tympanic membrane, ossicles, perilymph, and 
endolymph; and that the effective mechanism in the cochlea 
responds with due equivalence. Likewise it is easy to see 
that rapidity of vibrations could be accurately mediated 
by the several agents existing between the outer air and the 
receptive end-organ. Compound tones are, in harmonies, 
simply combinations of coordinated frequencies, or are, 
in the case of mere noise, just incoordinated frequencies of 
vibrations. And these coordinated or incoordinated fre- 
quencies of vibrations are picked up by the appropriate hair 
cells and so passed on to the cortex; in consciousness these 
vibration sensations may be perceived as a blended whole, 
or, if attention be paid to the individual sensations, the vari- 
ous constituents may be selected and referred with an accur- 
acy depending largely on one's auditory sense and education. 
This capacity for discrimination leads one to believe there 
must be a hair cell attuned for each separate rate of vibra- 
tions (pitch) throughout the limits of audition; moreover, 
there must be a cortical cell repository for each corresponding 
hair cell, with a specific individual fibril joining the two; 
else how could there be an awareness in consciousness of a 
definite distinction between two separate rates of vibrations? 
Evidence supporting both points is available. If the ear be 
slightly fatigued to a note of 360 vibrations, it manifests no 
fatigue to the immediate sounding of a note of 365 vibrations. 
If the apex of the cochlea is injured, the capacity for hearing 
tones of low pitch is lost, but if the basal portion be the part 
injured, capacity is lost for perceiving high tones. Again a 
sensory aphasia, affecting certain areas of the brain (superior 
temporal convolution) results in a more or less extensive inter- 
ference with the perception of sound, even though the 
mediating apparatus be functionally perfect. 



The limits of hearing are fairly well defined. To most 
people the lowest rate of vibration perceptible as a distinct 
tone is 30 a second; though some ears hear and appreciate 
the great-organ 64-foot pipe which produces but 16 vibra- 
tions a second, while to others these slow vibrations are 
felt as rather disagreeable pressure pulsations instead of 
being heard as a distinct note. The uppermost limits of 
audibility are about 40,000 vibrations a second, though 
many people are unable to hear this pitch at all. However, 
no such shrill note may be said to possess musical qualities, 
at least for the human ear. The highest note used with the 
piano is C 5, corresponding to 4224 vibrations a second, 
while the piccolo uses D 5 corresponding to 4752 vibrations 
a second; neither of these high notes possess much musical 
quality. The musical scale for all instruments is limited 
to about 7 octaves. The average individual human voice 
in singing uses a range of about 2 octaves, and the limits 
of the human voice in general from bass to soprano is about 
3 octaves. 

Harmonious tones are those whose rates of vibration, 
whether of their major tones or overtones are such as admit 
of frequent synchronizing; while discords are produced by 
those tones whose vibration rates permit of but partial 
synchronizing, and then at such periods as to alternately 
nullify and exaggerate each other. The physical explanation 
of this seems to be when two tones have synchronous periods 
of excursions— when the condensations and rarefactions 
coincide in time— the resulting effect on the ear is conson- 
ance; but when two tones have irregular periods of excur- 
sions—when the successive condensations and rarefactions 
of the two tones do not coincide in time— the resulting effect 
on the ear is dissonance; and in dissonance the alternation 
of effects produced on the ear by the nullification of sound 
(when a condensation coincides with a rarefaction) and the 
sharp amplification (when there is a coincidence of the con- 
densation waves of the two tones)— this alternation of silence 
and sound gives the disagreeable jar to the auditory mechan- 


ism known as a ''beat." The number of beats in a second 
will be the same as the difference in vibration frequency of the 
two tones, increasing directly with the degree of variation. 
When the number of beats equals 33 a second, the dissonance 
is decidedly disagreeable, becoming less so with sequent 
increase, and finally becoming scarcely noticeable when the 
number of beats rises above 132 a second. 

The most complete consonance is obtained from two tones 
of identical vibration frequencies, or from two tones whose 
frequencies bear the ratio of 1 to 2 (the octave), or 1 to 3 
(the twelfth), or 1 to 4 (the double octave). Harmonious 
combinations, though not of perfect consonance (largely 
because of overtones), have the vibration ratio of 2 to 3 
(the major fifth, C to G), or the ratio of 4 to 5 (the major 
third, F to A). Slightly less consonant are the major sixth 
(3 to 5, C to A), the minor third (5 to 6, A to C) and the 
minor sixth (5 to 8, E to B). Three or more notes bearing 
any of the sequent relations give the sound of a chord, as, 
for example, the major chord is composed of tones having 
the vibration ratios of 4 to 5 to 6 (C to E to G), or the minor 
chord is composed of tones having the ratios of 10 to 12 
to 15 (Fto AtoE). 


In the perception of sound, consciousness does not refer 
the sound to the immediate area at which the sensation 
arises, but projects it outward to the assumed physical 
source of the sensation. This habit of projecting the percep- 
tion probably arises from association experiences, it being 
fairly presumptive that one who had never heard sound 
would not project the sound when first perceived, but only 
gradually as he learned and came to realize the disjunct 
source. But though consciousness readily projects the 
perception of sound, it does not so readily locate its source, 
as any one may testify who has attempted to determine the 
whereabouts of an elusive cricket. One judges the approxi- 
mate location of sounds by noting the relative distinctness 
as seemingly affected by variations in the position of the head. 



Apparently there may be a slight difference in the intensity of 
the sound when both ears are not affected equally; then, 
by giving attention to which ear appreciation is the more 
delicate, one arrives at an approximate idea as to the direc- 
tion from which the sound proceeds. Also, the relative 
distinctness lends itself somewhat to an idea of the distance 
of the source of the sound. All of these judgments are 
deeply affected by visual judgments— of the retina, the mus- 
cles of the iris, and the ocular muscles. It is probable, 
also, that distances of faint sounds may be partially estimated 
by varying tensions of the tympani muscles. 


Although these organs are so closely linked with the organ 
of hearing, both anatomically and phylogenetically, the 
present opinion is that they are not concerned with audition 
at all, but with the perception and maintenance of the body's 
spatial position and relationship. 

It will be noted from an anatomical study of these struc- 
tures that the semi-circular canals are placed within the 
petrosa in approximately the three planes of a solid, so 
that movements of the head in any direction would involve 
a movement in the plane of any one canal, or in the parallelo- 
gram-diagonal of any two planes (Fig. 78) . Each membran- 
ous canal expands at its lateral termination in the utricle 
into an ampullated extremity within which certain termina- 
tions of the vestibular nerve come into relationship with 
hair cells. These latter hair cells project into a semi-gela- 
tinous substance lying free in the endolymph of that part 
of the canal. From which mechanical arrangement it follows 
that the hair cells would be easily affected by slight variations 
of intracanalicular pressures, especially since the gelatinous 
substance in which the hairs are embedded may be assumed 
to possess both elasticity and compressibility. Owing to 
its static inertia, the endolymph tends not to follow the 
planal movements of the canals, and there naturally results 
a change of pressure in the ampulla, positive when the planal 
movement of the endolymph is toward the ampulla and 



negative when the movement is in the opposite direction. 
In either case, an impression will be made on the gelatinoid 
substance embedding the neural hairs, and whether the 
gelatinoid response be expansile or contractile, there will 
ensue a stimulation of the hair cells somewhat analogous to 
pressure stimuli of the tactile hairs in the skin; indeed it is 

Fig. 78. — Figure from Ewald showing the situation of the three semi- 
circular canals in the skull of the pigeon. (Cunningham.) 

possible that different qualities of stimuli may be produced 
by whether the pressure phase is positive or negative. 
These stimuli affect the vestibular nerve, setting up impres- 
sions of which the majority are conveyed to Deiter's nucleus 
and thence to the cerebellum for those coordinated reflexes 
inductive of adequate muscle readjustments. Such few 


impressions as ascend to consciousness give rise to concepts 
of change in the position of the head. Thus it is that the 
head cannot be shifted in any plane, or in any diagonal of 
two or more planes, without producing an immediate read- 
justment of the muscles to meet the new condition. 

In the antero-inferior part of the utricle, and also of the 
saccule, is an area termed the macula. Here terminate 
other fibers of the vestibular nerve in a manner similar to the 
terminations in the ampullae of the semi-circular canals, 
except in addition there are here embedded in the gelatinoid 
material with the hairs a considerable number of minute 
crystals of calcium carbonate. These would seem to act 
through the force of gravitation on the hair cells of the saccule 
and utricle with variations of stress according to the position 
of the head, and hence would arouse stimuli apprising both 
consciousness and the muscle reflexes of the present position 
of the head. This function would be related to static con- 
ditions, as contrasted to dynamic variations mediated by the 
hair cells of the semi-circular canals. It might seem that 
movements of the endolymph in the utricle and saccule would 
be registerable also ; but, since these are ellipsoidal containers, 
the movement sensation might not be aroused so much by 
rotational movements like those in the semi-circular canals 
as by translational movements of the body, as in direct 
progression along horizontal, perpendicular, or oblique planes. 

The several varieties of movement mediations may be 
indicated as follows: nodding movements, as of affirmation, 
induce pressure variations in the anterior canals chiefly, 
though in part in the opposite posterior canal; movements 
of negation are mediated through the external, or horizontal, 
canals; nodding movements as of drowsiness— that is, 
laterally and backward— in the posterior canals chiefly; 
intermediate movements, in the resulting parallelogram- 
diagonal of any two planes, or a suitable combination of 
canals; simple alteration of position in a horizontal or vertical 
plane, by the hair cells of the utricle or saccule, or by both 
if the motion be compound. Of course, in complex move- 
ments, all the canals and accessory structures may be 


These data indicate that the labyrinth is an actual sense 
organ whose function is to accurately orient the head and 
body— that is, an organ of equilibration. This function 
produces important secondary effects on the muscles. The 
position of the body in space is not exactly identical in any 
two consecutive moments; whence it follows there must be 
a continuous stream of impulses from the labyrinth flowing 
into the reflex centers in the cerebellum, and resulting motor 
reflexes to the muscles; this produces those muscle contrac- 
tions necessary for adequate adjustment. But incidentally 
it produces another important result, this constant stream 
of impulses into the musculature of the body acts strongly 
in maintaining the normal tonicity of muscle; a result that 
may be demonstrated experimentally through cutting of 
the vestibular nerve; after such an operation the muscles 
tend to become lax and flaccid. 

These several functional points have been deduced as a 
result of extirpation and stimulation experiments on animals 
—mostly on pigeons, because of the relative accessibility of 
their labyrinths; but also on dogs and other mammals. 
Variations in the observed results are due apparently to 
genetic divergencies in the relative delicacy of coordination 
requisite for particular movements. The cutting of a canal 
is always followed by augmented homolateral movements 
of the head in the plane of that canal, probably because of 
unbalanced action to the opposite muscles of the head and 
trunk. Section of homologous canals on both sides is 
followed by exaggerated movements in that plane, probably 
because of reflex attempts to adjust the position of the head 
to the normalizing impressions from the eyes. If all the 
canals are severed, the animal is unable to maintain itself 
in a normal position. This result is explained as follows: 
The usual vestibular impulses not reaching the cerebellum, 
the animal is unable to coordinate its muscle activities to its 
needs; hence, it is unable even to stand unless supported, 
while if it attempts to walk, its movements are so forced 
and disordered that it sprawls and falls; if it be a pigeon, 
on attempting to fly, it somersaults through the air; if it be a 
fish, it progresses through the water on its side, or even in an 
inverted position. 


These incoordinations last a varying period, depending 
somewhat on the extent and severity of the operation. 
The animal may gradually, though but partially, regain some 
of its apparent normality, but this is because it learns to 
substitute tactual and visual sensations for those of which it 
has been deprived. Bandaging the animal's eyes brings on a 
resumption of the symptoms in all their initial severity. It 
should be added that muscle tonicity is never wholly regained, 
the neck muscles, especially, remaining permanently below 

Inasmuch as very similar results are obtained from 
cocainization of the ampullae it would seem that the effects 
are due to entire cessation of sensory impulses, and not, as 
some writers contend, to abnormal impulses arising from the 
operation, even though some abnormal sensations might 
readily arise during the retrograde process. 


Parker and Stabler: Distinction between Smell and Taste, Am. Jour. 
Phys., 1913, 32, 230. 

Lashler: Muscle Sense, Am. Jour. Phys., 1917, 43, 169. 

Landstroth: Referred Pain, Arch. Int. Med., 1915, 16, 149. 

Cannon and Washburne: Hunger and Appetite, Am. Jour. Phys., 1911, 
29, 411. 

Hardesty: The Role of the Tectorial Membrane in Hearing, Am. Jour. 
Anat., 1908, vol. 8. 

Schaeffer, J. P. : The Nose and Olfactory Organ, 1920. 

Carlson: Control of Hunger in Health and Disease, 1915. 



A VERY close correlation exists between the faculties 
of audition and vocalization, a vast number of auditory 
memories being associated with perceptions symbolizing 
speech. Many animals possess vocal powers of rather 
extensive connotability, but the specific combination of 
vocalization with those multiple modifications producible 
by movements of the lips and tongue is a faculty-complex 
considered peculiar to man, or the Primates. 

Vocal sounds are produced primarily in the larynx by 
the impingement of an expiratory blast of air upon the vocal 
cords. In such respect there is a marked similarity to the 
effect produced by an air blast in a combination reed and pipe 
musical instrument; but, whereas in the latter, variations in 
pitch may be secured by a lengthening of the column of 
vibrating air, in the larynx the changes in pitch are largely 
produced by variations in the relative tension of the vibrating 
cords, with a possible additional alteration through segmental 
vibrations of the cords. 

The vocal cords are two apposed strands of fibrous tissue 
stretched antero-posteriorly across the superior aperture 
of the trachea in a special structure called the larynx. The 
anterior attachment is on the posterior aspect of the thyroid 
cartilage; the posterior attachment is to the mesal aspect 
of the vocal portion of the arytenoid cartilages. Therefore, 
contraction of the crico-thyroid muscle, by drawing the cri- 
coid backward, tightens the vocal cord and thereby raises 
the pitch; the normal elasticity of the ligaments, aided by 
the contraction of the tkyro-arytenoideus externus, secures 
an adequate return to the normal position. An additional 
factor in effecting alterations of pitch is probably found in 
the internal portion of the thyroid-arytenoid muscle, which is 
sometimes termed the musculus vocalis. When present, it 
runs as discrete fibers from the inner lateral portion of the 


thyroid cartilage to be inserted at intervals in the lateral 
aspect of the vocal cord; tension of the individual fibers of 
this muscle would have the effect of fret stops on the cord, 
and would give similar variations in vibration frequency thus 
producible on the violin, for example. Other factors in 
modifying pitch are the lateral crico-arytenoids, assisted by the 
oblique and transverse arytenoids; these, especially the first, 
pull the vocal portion of the arytenoid cartilages into close 
approximation, thereby damping the posterior portion of the 
vocal cords. 

The posterior crico-arytenoids, though constantly active 
in enlarging the respiratory portion of the glottis during 
inspiration, are also concerned in enlarging the rima in the 
production of low tones. 

The Pitch.— The pitch, then, of the human voice, is chiefly 
dependent on the relative tension of the vocal cords, and the 
extent of the cord that is in vibration, both transversely and 
longitudinally. In lowest tones, both the major width and 
length of the cords vibrate, with the cords at their maximum 
laxity. With the gradual heightening of pitch, there is 
increasing tensity and steady approximation of the cords, and 
a limiting of the vibrating portion toward the mesal edge. 
Increasing the tension of the cord may make it actually longer 
with some higher notes than with lower ones, but this is more 
than compensated by the increased rapidity of vibration 
occurring always with an absolute increase of tautness. 
With further rise in pitch, the lengths of the cord are dimin- 
ished by approximation of the arytenoids, and by the stop- 
action of the internal thyro-arytenoids, until finally, with 
the high-pitched falsetto tones, but a relatively small portion 
of the anterior part of the cords is in vibration. 

The normal differences in pitch between the male and 
the female voices, or between the child and the adult, are due 
chiefly to the relative lengths of the vocal cords. The child's 
vocal cords are from 6 mm. to 8 mm. in length, with a slightly 
narrower range in compass for the boy than for the girl. 
At puberty the larynx develops rapidly; the vocal cords in 
the female increase to about 12 mm. to 15 mm. with an 
accompanying development of richness and power; in the 
male at puberty the increase is more marked and rapid, 


becoming from 16 mm. to 22 mm. in length. Inasmuch as 
new muscle-tension memories must be developed at this 
time, a voluntary control of the vocal organs is incomplete 
during the pubertal period; and in the case of the boy, 
in only about one-fourth of the lad's compass can notes be 
held with sufficient steadiness for use in music. 

Like any other muscial instrument, the human voice may 
vary in loudness and timbre, as well as in pitch. Loudness 
of tone is due primarily to the amplitude of vibration, and 
this is chiefly regulated by the strength of the expiratory 
blast, the cords being held meanwhile by special muscles at 
constant tension. With this increase of pressure against the 
cords, there is a constant tendency for the cords to elongate, 
and a related tendency for a greater transverse portion of 
the cord to participate in the vibration; this necessitates 
increasing activity of the muscles controlling the selected 
pitch, and not infrequently this results in a slight over- 
activity of the compensating muscles so that a singer tends 
to sharp his notes in a strong crescendo effort. 

Timbre.— The timbre or quality of the voice is chiefly due 
to the resonating air in the accessory respiration apparatus. 
Of themselves, the vocal cords do not give a strong note, but 
when the columns of adjacent air vibrate in unison, the rela- 
tive loudness of the original note is much amplified. Reso- 
nating chambers exist both above and below the larynx. 
Those below the larynx are contained in the trachea and 
bronchi; these vibrate with notes of the lower register, form- 
ing the so-called chest tones. Those above the larynx con- 
sist of the air spaces of the nose, naso-pharynx, pharynx, 
and mouth; these vibrate most markedly with notes of the 
upper register, forming the so-called head tones. Resonators 
in both regions may be called into use with tones of the middle 
register. These resonating columns of air vibrate in the 
frequencies of both the original tone and in those of sundry 
overtones, and thereby give individual characteristics to the 
human voice, inasmuch as no two individuals would probably 
have the same configuration in the bounding surfaces of the 
resonating areas— the larynx below the vocal cords varies 
in both size and shape, tracheas are of different length, 
bronchi are of different sizes and are placed at different angles, 


the supralaryngeal spaces show marked variations in size, 
shape and contour, and in their relative cubical capacity— all 
of which factors modify the production of overtones. And it 
has been well said that the vocal teacher's chief task consists 
in so training the pupil as to utilize most completely and 
effectively the several resonating columns of air, thereby 
adding as rich and full a variety of overtones as possible. 


Speech is a modified vocalization, so developed that various 
alterations and interruptions of tones have acquired definite 
connotations, varying of course with the language spoken. 
The fundamental tones in speech are the vowels, primarily 
formed by simple vibrations of the vocal cords, modified 
by the relative position of the tongue in the mouth; all vowels 
have a more or less musical quality. The difference in tonal 
quality, whereby one vowel is distinguishable from another, 
is produced by altering the resonating overtones, in the mouth 
chiefly. The richest and fullest vowel, the one requiring 
largest resonance in the buccal cavity as indicated by com- 
plete depression of the tongue and some extension of the lips, 
is the vowel u pronounced like oo. The variation from full 
tones to thin ones, produced by a progressive lessening of the 
buccal resonance through a gradual elevation of the tongue, 
is as follows: long o, a pronounced ah, i as ai, long a as in 
face, long e. 

The consonants are produced by modifications of the 
expiratory blast at different points, as it passes through the 
buccal cavity, so as to produce constrictions or interruptions. 
Proceeding from before backward, according to the means of 
modification, the consonants of the English language may be 
listed as follows: labials, with lips opening, b, p; labial, with 
lips closing, m; labio-dental, opening, v; labio-dental, closing 
/; linguo-dental, opening, t, d, rolling r; linguo-dental, closing, 
/, n; anterior linguo-palatal, sibilant opening, soft c, z; anterior 
lingtio-palatal, sibilant closing, s; ]xjsterior lingvo- palatal, 
j, g; iivalo-lingual, hard c, hard ch, hard g, k, q, (German r) ; 
uvalo-lingual, sibilant, x; uvalo-lingiio-yiasal, final ng, (French 
final en). 


The eye is the end-organ of vision; it consists of two dis- 
tinctly separate physiological mechanisms, one having to 
do with the convergence of light rays from the exterior to the 
retina, and the other concerned with the transmutation of 
radiant energy into neural energy. These two mechanisms, 
with their accessory structures may well be considered in the 
same sequence followed by light in passing through and to 
the several structures. 

Rays of light, in passing to the retina, traverse structures 
having curved surfaces, and hence are bent from a direct 
path; and they also pass through media of unequal densities, 
and are hence further refracted. The first curved surface 
on which the rays of light impinge is the cornea, which has 
an average radius of curvature of 8 mm. and an index of 
refraction of 1.33, air being taken as the norm. The index 
of refraction of the aqueous humor, lying between the cornea 
and the lens, is the same as the cornea so no further refrac- 
tion takes place until the lens is reached. The lens has a total 
refractive index of 1.437, with an average radius of curva- 
ture for its anterior surface of 8 mm., and for its posterior 
surface of 10 mm.; so the ray of light at the lens will suffer 
4 refractions, 2 due to the curved surfaces and 2 due to the 
alterations in density of medium on entering and on leaving 
the lens. The computation of the exact path of a ray of 
light from the cornea to the retina becomes therefore, a 
complicated geometric problem. Listing found, however, 
that a sufficiently accurate approximation of this path 
could be ascertained by assuming the total refraction to 
take place at a single convex surface separating the air from 
the humor of the eye, the humor and the convex surface 


having identical refractive indices and these being identical 
with that of the convex surface of the cornea. In such a 
schematic eye the ideal refracting surface lies 2.3 mm. 
posterior to the anterior surface of the cornea; and the center 
of curvature of this schematic refracting surface lies 7.3 mm. 
posterior to the anterior surface of the cornea, a point in the 
normal eye which would be located in the crystalline lens. 
Now by the laws of refraction the principal focal distance 
for this schematic refractive surface must lie 15.5 mm. 
behind the nodal point (i. e., the center of curvature), 
or 20.5 mm. from the schematic refractive surface, which 
would be equal to 22.8 mm. from the anterior surface of the 
cornea of the eye. It has been found that this principal 
focal distance of this schematic eye coincides with the retina 

Fig. 79. — Path of the rays in the formation of an image on the retina. 


of the normal resting eye; therefore, data obtained by 
experimentation with the schematic eye is applicable to the 
normal eye, and diagrams based on this deduction are 
adequate for an accurate representation of optical conditions. 

Such a diagram shows that rays of light from any point 
of an object may be drawn through the nodal point, and will 
result in a real image, inverted, and diminished in size 
(Fig. 79) ; that the further away may be the object the smaller 
will be the resulting image; and that no matter where upon 
the convex surface the rays may fall, they will be converged 
to the same point on the retina as will those rays which from 
the same area pass through the nodal point. 

When the object is brought toward the eye there is soon 
reached a point (about 5 meters) where the divergence of the 



rays is greater than the converging power of the refractive 
surface can overcome for the purpose of focusing, it being 
assumed there is a strictly uniform refracting surface. But 
in the human eye, an adaptive mechanism, the lens of the 







IRIS (ante 
nor surface) 












80. — The upper half of a sagittal section through the front of the eyeball 


eye, enables an increase in the power of refraction, so that 
objects may still be focused on the retina even if brought 
considerably nearer. The lens of the eye is an elastic, bicon- 
vex, disc-shaped body; it is kept in a somewhat flattened 
condition by^the compressing effect of the capsular membrane. 


This membrane is attached eireumferentially to the ciliary 
process to which also is attached the ciliary muscle (Fig. 80). 
When the radial fibers of this muscle contract, the sphincteric 
action pulls the ciliary processes centrally, thereby rendering 
the capsular membrane lax. The elastic lens, thus released 

Fig. 81. — Diagram illustrating the change taking place in the curvature 
of the lens of the eye when one focuses his attention on a near object; note 
that the variation in curvature takes place on the anterior surface, chiefly. 
This adjustment for near vision is wrought by a reflex contraction of the 
ciliary muscle (A); this produces a relaxation of the sling ligament (B), 
allowing the lens (C) to assume its normal more convex condition; this 
increase in the thickness of the biconvex lens results in a shorter focusing 
of the rays of light within the eye. 

from constraint, immediately becomes more convex, especi- 
ally on its anterior surface; and this increased convexity 
naturally heightens its degree of refractability (Fig. 81); 
hence, rays of light from a nearer source than is possible in 
the schematic eye are clearly focused on the retina, 


Still there remains a point at which the maximum of 
refrangibility is reached, even with the most elastic lens. 
This point is known as the near "point of distinct vision; 
it varies with age, steadily becoming further removed with 
the passing of years. The accompanying table gives a 
good estimate of the average rate at which the point of vision 

Range in 


Near point. 



7 cm. ( 2 . 76 in.) 



10 cm. ( .3 . 74 in.) 



14 cm. (5.61 in.) 



22 cm. (8.66 in.) 



40 cm. (15.75 in.) 



100 cm. (39.37 in.) 


Far Point of Distinct Vision.— The far point of distinct 
vision is theoretically infinity, inasmuch as parallel rays of 
light are accurately focused without effort on the retina, 
but objects much nearer are also focused without any 
effort of accommodation. It has been found that the practical 
far point {pundum remotum) from which rays of light are 
sufficiently parallel to be focused without effort is about 
8 to 10 meters. Of course these rays are not parallel, but 
the difference in size of the image on the retina when the 
focus is at 10 meters, or at infinity, is less that the width of a 
single rod or cone in the fovea. 

Size of Image on the Retina.— The size of the image on the 
retina varies according to the size and distance of the object, 
and may be readily computed when these two factors are 
known, since the ratio of the size of the object is to the size 
of the image as the distance of the object from the nodal 
point is to the distance of the image from the nodal point. 
This last, the distance of the retinal image from the nodal 
point is, in the normal eye, considered a constant factor, 
15.5 mm.; the determination of the size of the image, then, 
becomes a matter of computation; for example, a church 
spire 30 meters high is seen at a distance of 800 meters, 

1 A diopter represents the refractive power of a lens having a principal 
focal distance of one meter ; and since the power of a lens is expressed by the 
reciprocal, then a lens whose principal focal distance equals y^o meter is a 
lens of 10 diopters, 1 of 10 meters is a lens of 0.1 diopter, etc, 


then the size of the retinal image may be found by solving 
the following equation: 

30 : X : : 800 : 0.0155 x = 0.0058 

The smallest retinal image, perceptible as more than a 
mere point, is about 0.0043 mm., corresponding to a visual 
angle of about one minute. Experiment indicates that few 
people can appreciate two points of light when the subtending 
chord measures an angle of less than one minute. Inasmuch 
as the diameters of the retinal rods and cones in the region 
of the fovea measure between 0.002 and 0.005 mm. in diame- 
ter, this would indicate that a retinal image so small as to 
be impressed on but one rod or cone only would not give an 
optical sensation. 


Chromatic Aberration.— The splitting up of white light 
into its spectral colors when passed through a prism is a 
phenomenon of common experience. Since any medial 
section of the lens is a prism, it therefore tends to split white 
light in the manner of prisms in general. In lenses this 
aberration is corrected by combining flint and crown glass 
in such a way that the dispersive powers of one neutralize 
those of the other. No such arrangement is present in the 
eye, but the tendency to such an aberration is seemingly 
neglected by consciousness, possibly because the contrast 
of the strong, yellow, middle rays depresses the retinal 
excitability to the rays of the two extremes of the spectrum; 
then, too, the iris cuts off that part of the lens most refrac- 
tive. That an actual dispersion is produced in the eye is 
indicated by the fact that in looking at a violet spot and a red 
one in close apposition, a stronger effort of accommodation is 
required for focusing on the red spot than on the violet. 

Spherical Aberration.— The tendency of those rays of light 
passing through a lens near its periphery to converge to a 
focus sooner than those passing through the center is com- 
pensated in the human eye by two adaptive mechanisms. In 
the lens itself there is an increasing density of structure near 


the center with a consequent heightened refrangibihty; 
the curvature of the lens is also sharper at the middle of the 
lens than at the periphery, both of these arrangements are 
utilized in the manufacture of scientific optical instruments 
for overcoming spherical aberration. A further method, 
especially used in photography, is to interpose a diaphragm 
so as to limit the rays of light to the central portion of the 
lens; a similar arrangement is present in the eye as the iris. 

The Iris.— The iris (Fig. 79) is a prolongation of the choroid 
coat forward anterior to the ciliary processes where it hangs 
as a circular curtain in front of the lens. This curtain, or 
diaphragm, is pierced centrally by an aperture, the pupil, 
the diameter of which may be readily altered in response to 
different intensities of light. Constriction of the pupil is 
effected by circular muscle fibers, termed the sphincter 
pupillce; dilatation of the pupil is produced by contraction 
of the radial muscle fibers, termed the dilator pupillcB. 
The iris is more or less deeply pigmented, and thereby 
serves to shut off all those rays of light not passing through 
the mobile aperture, and as this aperture is anterior to the 
central portion of the lens, the refraction of light is largely 
limited to this area, and both chromatic and spherical 
aberration are thus largely prevented; then, too, lessening of 
the aperture increases the sharpness of the image on the 

The responses of the pupil may be grouped under two 
heads, contraction of the pupil, and dilatation of the pupil. 

Contraction of the Pupil.— Contraction of the pupil may 
be due to any of the following: 

(a) Relative increase in the intensity of light falling upon 
the retina. This constitutes the so-called ''light reflex;" 
it is probably due to retinal changes whereby a stimulus is 
sent, ma afferent fibers in the optic nerve to the superior 
quadrigeminate, thence to the motor oculi center in the 
mesencephalon and especially to the anterior portion of this 
center in which the pupillary nuclei are assumed to exist. 
It is maximal when the eye is exposed to bright light after 
having become dark-adapted, and under such conditions 
mav amount to as much as 8 mm. About 0.05 second inter- 


venes between the reception of the stimuhis and the response, 
and about 0.1 second before the maximum is reached. 

(b) The pupil may contract as a result of the coordination 
of action existing between the ciliary muscle and the iris; 
this is sometimes spoken of as the '^accommodation reflex." 
The ciliary muscle, it will be recalled, acts to produce 
increased convergence of the rays of light coming from near 
objects; this is accompanied by a constriction of the pupil 
which serves to sharpen the details of the image thrown on the 
retina, the relative diminution of light being compensated 
by the increased nearness of the object. This coordination 
is centric, there apparently being enough correlation of 
energy at the moment of initiation to produce a stimulation 
of both centers. A third factor here is the conjoined action 
of the internal recti muscles which produces the essential 
convergence of the visual axes. 

(c) The pupil may contract as a result of the relaxation 
accompanying sleep. This may be due in part to increased 
tonicity of the sphincter pupillce, and may be somewhat of an 
associated condition referring to the internal recti muscles 
since these muscles are more tonic during sleep than others of 
the eye. 

(a) The pupil may be contracted as a result of functional 
interference wrought by drugs, as, for example, by morphine 
which depresses the cervical sympathetic or by physostigmine 
which stimulates the terminations of the motor oculi. 

Dilatation of the Pupil.— Dilatation of the pupil may be 
due to the following: 

(a) Relative decrease of the intensity of light falling on the 
retina. Here, again, much depends on the degree of light 
to which the retina has become adapted. When two indi- 
viduals are brought into a moderately-lighted room, one from 
a dark room and the other from a brilliantly-lighted room, 
the iris of the former will contract while the iris of the latter 
will dilate; gradually, however, the alterations of each will 
pass off, and in from five to ten minutes their pupils will be 
approximately alike. The reflex path, in dilatation of the 
eye, is assumed to be by afferent fibers from the retina, via 
the optic nerve to the superior quadrigeminate, and thence 


to the unknown nucleus of the cervical sympathetic which 
controls the dilator pupillee. 

(b) Strong sensory impressions, and 

(c) Strong emotional excitement like fear and rage. 

Both cause dilation of the pupil through reflex stimula- 
tion of the sympathetic portion of the autonomic system, 
with an accompanying inhibitory effect on the cranial 
division; consequently the dilators, coming from the cervical 
sympathetic, are stimulated while the tectal constrictors are 

(d) The pupils are dilated when there is functional inter- 
ference wrought by drugs; as, for example, when atropine 
paralyzes the sympathetic terminals of the third nerve, or 
when epinephrin stimulates the cervical sympathetic. 


Myopia.— It has been pointed out how parallel rays of 
light come to a focus on the retina without influencing the 
mechanism of accommodation, and how rays of light lying 
within the punctum remotum are further refracted by the 
increasing curvature of the lens to the end that the several 
rays may become properly focused on the retina. Not 
infrequently one finds eyes in which there is some abnormality 
in the shape of the eyeball or in the curvature of the refract- 
ing surface (Fig. 82). In some cases the axial diameter of 
the eye is too great, and the rays of light are focused ante- 
rior to the retina, that is, the retina is further away than the 
focal distance of refraction of the lens and cornea; this results 
in a diffusive blurring of the image, and is the condition 
known as near-sightedness or myopia. This condition is often 
caused by excessive muscular effort to secure accommodation 
for objects too near the eye, and the resulting increase in 
intraocular tension tends to elongate the eyeball. In rarer 
instances, myopia may be due to abnormally high curvature 
of the cornea or lens. In any of these cases, the therapeutic 
recourse is an accessory concave lens which will disperse 
the rays of light somewhat before they impinge on the cornea. 


Hypermetropia.— In hypermetropia, or far-sightedness, a con- 
dition opposite to myopia prevails. Either the curvature of 
the refracting surfaces is too low, or much more frequently 
the eyeball is so small that the principal focal distance of 
the lens lies posterior to the retina; this condition induces a 
blurring of all near images, and an unusual accommodative 
effort with even distant objects (Fig. 82, B). In such cases, 
the near point of vision is much farther away than in the nor- 

FiG. 82.— Diagrams of course taken by parallel rays in entering normal 
(emmetropic) eye (A), hypermetropic eye (B), and myopic eye (C). 

mal, or emmetropic eye, since it is necessary to bring the 
muscles of accommodation into action even with parallel 
rays. The principal recourse in these cases consists in the 
use of convex lenses whereby to increase the possibility of 

Presbyopia.— A condition dioptrically akin to hyperme- 
tropia is presbyopia or old-sightedness. In this condition the 
near point of vision recedes steadily, and the elderly person 
has to adopt convex lenses to permit of close use of the eyes. 


The assumption in presbyopia is that there is a gradual 
diminution in the elasticity of the lens of the eye, so that the 
effort of accommodation becomes increasingly ineffective. 
Presbyopia comes on at a later day in myopic eyes than in 
h^^permetropic, inasmuch as the effort of accommodation 
is less; sometimes, in fact, the gradual flattening of the lens 
in a presbyopic myope results finally in an adjustment where- 
by the refraction focus equals the diameter of the eyeball. 

Astigmatism.— Another form of defect is where the cornea, 
or where one surface of the lens, instead of being a perfect 
segment of a sphere possesses some inequality of surface 
curvature, that is, different quadrants, or even different 
meridians, do not have identical radii. Hence the centers of 
curvatures of any two areas from this segment of a spheroid 
will not be a point but a curved line instead, and the principal 
foci of different segments of the convex surface will not be 
in the same spherical surface but will be in the surface of a 
conical projection. The obvious recourse in this condition 
is a lens so ground as to make such adequate compensation 
for divergence or convergence as the abnormal area of the 
segment may demand. This condition of abnormal curva- 
ture of the refractive surface is known as astigmatism. 

Intraocular pressure is a hydrostatic condition, serving 
to maintain the essential sphericity of the eyeball. The 
water content is supplied from the capillaries of the choroid 
coat, while the narrow avenue of escape is through the 
canals of Schlemm (Fig. 80). 


The radiant energy termed light is assumed by physicists 
to consist of transverse vibrations of the ether, traveling at 
the rate of 186,000 miles a second, and having wave lengths 
varying from more than 800 millimicrons to less than 300 
millimicrons. In that portion of the solar spectrum which 
excites the retina, the wave lengths in the red are about 0.760 
microns while those in the violet end are about 0.397 microns. 
It is well known there are many rays beyond the limits of 
vision, as shown by heat registrations in the infra-red region. 


and b}' actinic effects on sih'er salts in the ultra-violet region. 
A point of considerable interest is that wave lengths in the 
violet end measuring down to 0.313 microns become visible 
after removal of the lens in cataract. 

These various rays, as reflected from sundry objects and 
surfaces, are converged by the refracting mechanism of the 
eye onto the retina where they set up molecular vibrations 
in the retinal cells, thereby initiating neural impulses. What 

limitans interna ••■ 
Stratum o'pticum — 

Ga ngl ion ic layer-- 

Inner plexi'form ,,_ 

Centrifugal fibre ■' 

Inner nuclear 

Fibre of Muller - 

Outer plexifmm . 


Outer nudear _) 

limitans externa 

Layer of rods _ 
and cones 

\ <=>\ o I o I o I o I 

Fig. 83. — Plan of retinal neurons. (After Cajal.) 

Diffuse amacrine 

•'■Amacrine cells 

••'Horizontal cell 

-;Rod granules 
^'^Cone granides 

o \'B''\ ' Pigmented layer 

may be the nature of this transmutation is unknown, but 
certain facts have been ascertained, a consideration of which 
helps toward an understanding of what may be the process. 
It is highly presumptive that the immediate effect of 
the vibratory energy of light is primarily received in the rod 
and cone prolongations of the visual cells (Fig. 83), and 
that in this vicinity exists the peculiar adaptation whereby 
one form of energy is converted into another. The most 


favorably considered explanation of the mode of this con- 
version is the photographic theory in which it is assumed 
that the rhodopsin or 'Visual purple" is decomposed by the 
light rays, and that from this chemical action a secondary 
neural action is generated. The widespread presence of 
rhodopsin in the retina, and the manner in which it seems 
to accumulate among the rods and cones when the eye is 
protected from the light, seem to be confirmatory evidence. 
But there is no rhodopsin in the most sensitive part of 
the retina, the fovea centralis, nor in the eyes of birds; so 
other students have suggested that the rhodopsin serves 
chiefly as an absorption medium to prevent refraction and 
diffusion in the more dense portions of the retinal layers, 
and is not needed in the fovea because here the refracting 
ganglion cells do not lie in the direct path of the light rays. 
Possibly, moreover, an intermediate chemical reaction is not 
essential for the induction of a neural discharge; radiant 
energy impinging on the warm spots of the skin initiates 
neural currents directly, and it may be that an analagous 
selective receptivity exists in the rods and cones of the retina. 

The retina is not equally sensitive throughout its extent. 
Vision is most perfect in the fovea centralis. The fovea 
lies in the direct field of the principal optic axis; here are 
cones only, and they with their nuclear attachments are 
exposed to the immediate action of the rays of light, while 
the neural and ganglionic layers, which in the rest of the 
retinal field intervene, here lie circumferential to the chief 
line of vision. On the fovea centralis are converged all 
images of whatever may be occupying one's critical inspection 
since here as nowhere else in the retina is ocular sensation 
so discriminatingly received. 

Surrounding the fovea centralis is the macula lutea (Fig. 
84). This area contains both rods and cones, each cone 
being surrounded by a layer of rods; interposed in the line 
of sight are several layers of ganglion cells, yet vision here 
is more distinct than in any other portion of the retina 
except the fovea. About 3 mm. to the nasal side of the 
macula lutea lies the exit of the optic nerve (Figs. 84 and 85), 
at which point (with an area of about 2.5 the only 


Optic disc 

Macula lutea 



Fig. 84. — Interior of posterior half of bulb of left eye. The veins are darker 
in appearance than the arteries. (Gray.) 







Fig. 85. — The terminal portion of the optic nerve and its entrance into the 
eyel)an in horizontal section. (Foldt.) 


retinal elements are the axons of the ganglionic cells; hence, 
at this point vision is absent, and the area is known as the 
''blind spot.'' The balance of the retina, as far out as the 
ora serrata, is occupied by an excess of rods over cones. 
Throughout this region images are perceived with less 
distinctness than elsewhere in the retinal field, yet with 
sufficient clearness to keep us fairly well apprised of such of 
the immediate environment as may be comprehended in the 
visual field, especially if a movement takes place outside 
the field of immediate attention yet within the scope of the 
outer rods. In dim lights, and in the dark-adapted eye, 
the circummacular field seems to be more sensitive to the 
relatively feeble stimulations than do other portions of the 
retina. Several studies indicate that the rods of the retina 
are chiefly concerned in the mediation of gradations of light, 
while the cones are also sensitive to color variations. 


Within certain limits, Weber's law (in relation to propor- 
tionate increments of stimuli for evoking successive sensory 
responses) seems to hold good for the function of vision. In 
the case of white light Starling assigns the ratio of 0.01; 
that is, the eye would register a difference of sensation 
between twin lights where one was of 50-candle power and 
the other was but J-candle power more or less. The ratio 
will not hold good at either of the extremes, of distance or of 

This power may vary somewhat in relation to the spectral 
colors of the illuminant, inasmuch as the retina is much more 
sensitive to the light rays from the middle of the spectrum 
than to rays from more lateral areas. Assigning to yellow 
the relative luminosity of 1000, then that of the other colors 
of the spectrum is about as follows: reddish yellow, 780; 
green, 370; orange, 128; red, 22; blue, 8; violet, 1. 

The sensation, or rather the excitation, produced in the 
retina is of longer duration than the period of the stimulus. 
This definite though transient persistence of the sensation 
admits of a perception of actual continuity whenever the 


succession of stimuli is at the rate of one every one-twenty- 
fifth of a second. Consequently a compounded disc, rotating 
at this or a higher speed, gives a fusion in perception of the 
sensations aroused, and one perceives a combination effect 
instead of the component factors— a phenomenon commer- 
cially exploited in the ''movies." 

With too persistent fixation upon any bright object there 
quickly supervenes a condition of fatigue; and though this 
fatigue may not be perceived as such directly by conscious- 
ness, yet it is made known by contrast. When an eye is so 
fatigued, and is directed at a plain white surface, the remain- 
ing portions of the retina send in normal impressions of this 
white area, but the fatigued fovea can send but subnormal 
impressions and these give in consciousness a contrasted 
percept of a seeming dark area of equivalent size and shape 
to the preceding bright one. 


When a beam of sunlight is passed through a suitable 
prism its several rays are dispersed at different angles, with 
the result that the entering pencil of light emerges as a 
varicolored band. In this band it is customary to find 
six fundamental colors: red, orange, yellow, green, blue, and 
violet; though as many as 26 monochromatic colors may be 
detected when the spectrum is studied over limited fields, 
while as many as 165 shades have been found by Konig. 
Extensive studies made of these phenomena indicate that the 
spectrum is due to a difference in wave lengths of the several 
rays, the longer red waves having less refrangibility than the 
shorter violet. It would seem that each pure color has a 
definite wave length, indicative of the vibration period of the 
incandescent atoms giving rise to those movements in the 
ether. The approximate relative wave lengths of the six 
spectral colors are stated as follows in millimicrons: Red, 
750; orange, 620; yellow, 587; green, 518; blue, 460; violet, 
396. A certain difference in wave length is necessary to 
give an impression of difference in color, varying considerably 


with the portion of the spectrum under observation. To give 
a distinct variation in the quality of the sensation produced 
there must be a difference in wave length of about 4.7 milli- 
microns at the red end, from 0.7 to 2 millimicrons near the 
middle of the spectrum, and about 0.5 millimicrons at the 
violet end. 

The appearance of the spectrum varies a great deal accord- 
ing to the relative amount of daylight. As twilight comes 
on the extent of the red end gradually lessens from the left 
and the maximum luminosity seems to shift from the yellow 
to the green; later, reds and violets disappear entirely, then 
the greens, and finally the blues. 

Some strange and curious phenomena result from combina- 
tions of the monochromatic spectral colors. If, by means of 
suitable prisms, the alternate colors are combined, the 
resulting color is like the intermediate one; but the combining 
of certain other colors give white instead, as for example, 
the combining of red and greenish blue, orange and cyan blue, 
yellow and indigo blue, greenish-yellow and violet. When 
colors further apart than these complementary colors are 
combined, they produce the extra-spectral color purple. If 
all the colors of the spectrum are fused, the result is a white 
light. This is all very remarkable. Orange, for example, has 
a wave length of 620 millimicrons; yet an orange light is 
produced when a red light of 750 millimicrons is mixed with 
a yellow of 587 millimicrons; how can this be possible, either 
physically or physiologically? We do not know. 

Another problem: If the two spectral lights, orange and 
green be superposed, the result so far as the eye can see is the 
production of a pure yellow; but if this synthetic yellow light 
be passed through another prism, it emerges like the original 
orange and green. On the other hand, if the band of mono- 
chromatic yellow in the first spectrum be passed through a 
second prism, it emerges a pure yellow. So far as the eye 
can detect, the synthetic yellow formed by the fusion of 
orange and green lights is identical in quality with spectral 
yellow; but the second prism proves they are not identical 
physically. What is the explanation? 

The problem becomes even more difficult when we endeavor 


to ascertain what is the nature of white Hght. If the three 
colors, red, green, and violet, be mixed in suitable proportions, 
the resulting blend is a white light; but by mixing them in 
other proportions it is possible to obtain any of the spectral 
colors or shades, or even the extra-spectral color purple. 
The same results ensue from suitable mixtures of red, yellow, 
green, and blue lights. The physical reasons for these phe- 
nomena are unknown; and as the retina seems unable to 
resolve white light into its spectral components, a physiologi- 
cal explanation does not appear possible at present. 

It should be noted that these various color effects are 
produced by the colored lights obtained from a dispersion of 
sunlight, and are not duplicable with pigments. Whereas 
the mixture of spectral indigo-blue and spectral yellow gives 
a white light, the mixture of yellow and indigo pigments 
gives a green color. The explanation for this is that yellow 
pigment reflects some red and green light besides its dominant 
yellow, but absorbs the blue and violet rays in the sunlight; 
and the indigo pigment absorbs red and yellow, but reflects 
green and blue; therefore when the yellow and indigo pig- 
ments are mingled, the only color in the sunlight not absorbed 
by the mixture is green, and this being reflected gives the 
appearance of green to the combination. 

This experiment involves the subjective side of color, 
or color as a sensation. It is assumed that the nature of a 
color, from the physical standpoint, is due either to the 
presence of a diffractive surface, as in the feathers of a cock 
pheasant, or, more widely, to the presence of absorptive 
pigment whereby some wave lengths of solar light are retained 
while other wave lengths are reflected. According to this 
assumption the color of an object consists of such rays as 
are reflected from its surface; an object has the color of orange, 
for example, because it is reflecting solar wave lengths of 
620 millimicrons, and absorbing all other wave lengths. 

The subjective side of color consists of the sensation 
produced when uniform waves, or multivarious combinations, 
impinge on the retina. Concerning what takes place in the 
retina little is known; and it is necessary to study chiefly the 
effects produced in consciousness, with the hope that from 



these introspections there may be evolved some more-or-less 
plausible hypothesis. 

Two theories of color-vision have aroused wide discussion 
and speculation, though they have not been generally 
accepted because neither one explains all the phenomena. 
These theories are the Young-Helmholtz and the Hering. 

The Young-Helmholtz theory of color vision assumes that 
there are three fundamental color sensations, red, green and 
violet (Fig. 86); and that these sensations are produced in 
the cones of the retina, through selective decomposition of 
hypothetical photo-chemical substances, by wave lengths 
of 750, 518, and 396 millimicrons, corresponding respectively 

Fig. 86. — Curves showing sensitiveness of the three varieties of nerve 
fibers to different parts of the spectrum. 1, red fibers; 2, green fibers; 3, 
violet fibers. (Young-Helmholtz theory.) (Starling.) 

to the red, the green, and the violet. It being demonstrable 
that from mixtures of these three fundamental colors all the 
other shades and tones of the spectrum, including white light, 
are producible, so in this theory it is assumed that the sensa- 
tions corresponding to different colors are due to propor- 
tionate decomposition of the photo-chemical substance in the 
retina by varying quantities or intensities of those several 
waves. White would be due to a simultaneous decompo- 
sition in the activity ratio of R = 18.6, G = 31.4, and 
V = 30.5; black w^ould be due to the absence of any activity, 
and hence an absence of sensation. In this theory, the 
synthesis of two or more stimuli must be centric. 


In the Hering theory six primary colors are arranged in 
constantly definite groups of two— the white-black group, 
the red-green, and the yellow-blue (Fig. 87). It is assumed 
that in the retina there are three types of photo-chemical 
substances, corresponding with the three groups of color. 
It is further assumed that some colors, the red, the yellow, 
and the white— have a decomposing effect on this chemical 
substance, while the other groups— the green, the blue, and 

Fig. 87. — Schema to illustrate the Hering theory of color vision. (Foster.) 
The curves indicate the relative intensities of stimulation of the three color 
substances by different parts of the spectrum. Ordinates above the axis, 
X-X, indicate katabolic changes (disassimilation) , those below anabolic 
changes (assimilation). Curve a represents the conditions for the black- 
white substance. It is stimulated by all the rays of the visible spectrum 
with maximum intensity in the yellow. Curve c represents the red-green 
substance, the longer wave lengths causing disassimilation (red) , the shorter 
ones assimilation (green.) Curve h gives the conditions for the yellow-blue 
substance. (Howell.) 

the black— have a reconstructive effect. Thus when red 
light, or yellow, or white, is acting upon the retina, katabolic 
changes are produced in the photo-chemical substance, with 
a concurrent stimulation of the retinal cells; but when green, 
or blue, or black impressions are on the retina, anabolic 
changes will take place in this substance; and these, too, give 
stimuli to the retinal cells. Intermediate shades and tones 
are produced by partial disintegrations or by blocked assimi- 


lations, together with the disassimilatory effect on the white 
substance assumed to be exerted by all the rays. 

Neither theory is satisfactory. The Helmholtz theory 
gives selective discrimination to the cortex instead of to the 
end-organ; it assumes no color is ever completely saturated, 
and its interpretation of the facts of color-blindness are 
inadequate (see infra). The Hering theory assumes a com- 
plete reversal of metabolic activity between the adjacent 
yellow and greens; it conflicts with general probability as to 
the non-sensibility of anabolism; it assumes an active sensa- 
tion going on as a result of the complete withdrawal of light; 
and it is inadequate for the explanation of color-blindness. 
Both theories are dependent on a hypothetical photo- 
chemical substance manifesting delicate affinities for light 
waves of different periods, whereas the most actinic of 
spectral rays are those very ones most absorbed by the lens 
and by the vitreous humor of the eye. Then, neither theory 
attempts to account for the real nature of white light, or to 
offer a suitable explanation why the sensation produced by 
mixing red and green lights should be the same as that pro- 
duced by the fusing of orange and blue, or why either of these 
combinations give the same sensation as that produced by the 
reassimilation of all the rays in the spectrum. It would 
seem that a simpler theory is demanded, one that will regard 
the cones as possessing a selective sensitiveness to particular 


This defect in the retina of the eye is probably always 
congenital. It may show a range of variability extending 
from the total color blind, with whom the world is painted 
solely in grays, up to those who show but a slight sub- 
normality in differentiating certain tones or shades. It has 
been estimated that as many as 20 per cent of all individuals 
are somewhat subnormal in the color sense, and that this 
ratio is relatively very much higher in the male than in the 
female. It has been asserted, also, that the defect is more 
common among the ignorant classes than among the more 
intelligent, but the apparent deficiency here may be educa- 


tional rather than optical. (The daughter of the writer, 
at the age of two years, could correctly assort eight different 
shades of eight different colors (64 in all), yet a playmate of 
five, known not to be defective in color sense, was unable 
to assort the shades correctly though showing no confusion 
with the primaries). 

According to both the Helmholtz and the Hering theories 
there would be but three types of color blindness— the total, 
the red-green, and the violet-yellow— with no intermediate 
possibilities, inasmuch as the complementary colors are 
either interdependent (Helmholtz) or antagonistic (Hering). 
This difficulty has led some students to abandon hypotheses 
in the consideration of color blindness, and to simply arrange 
a classification along clinically-observed facts. 

In such an arrangement, a normal person is considered 
hexachromic; that is, he will name six outstanding colors in 
the spectrum; occasionally is found a person of high color 
sensitiveness who is heptachromic, and who plainly sees 
indigo as a separate color band in the spectrum. Ranging 
below the norm are the penta-, tetra-, tri-, di-, and mono- 
chromics, according to what the observer sees in the spec- 
trum. A monochromic sees everything as gray, untouched 
with any tinge of color. A dichromic usually includes red, 
orange, yellow, and green, under a red monochrome, with 
the balance of the spectrum violet. A trichromic sees red, 
orange, and yellow, as pale orange, with a marked shortening 
of the red end, and also perceives green and violet. The 
tetrachromic usually sees red, yellow, green and violet. 
There are many varieties of the pentachromic; in the rarer 
cases, violet alone is not seen; there are more cases where 
the green is not apprehended; and there is a maximum of 
cases in which the sense for red is deficient. In the red 
blind, there is a lack of appreciation of the red end of the 
spectrum, those reds only being perceived which are brightly 
luminous with orange; with such an individual a rose color 
would be classed with the blues since the red component of 
the rose hue would be invisible. 

More w^idespread than is commonly recognized are those 
cases of color weakness in which there is a diminished sensi- 


tiveiiess to some color, usually red or green, and a relative 
inability to arrange colors by groups. This relative insensi- 
tiveness makes the eye slow to apprehend the red, for instance, 
a difficulty rapidly heightened by diminishing luminosity. 
Such a person sees all the spectral colors, shades and tints, 
but requires increased illumination to perceive the extreme 
red. His difficulty in classification seems largely to depend 
on two things : (a) A sense of color equality, whereby a tint 
is as distinct an entity as a spectral color; and {h) a lack of 
specific education. Not infrequently also there may be true 
perplexity, as when a certain shade of very dark red is 
confused with a deep brown green. 

In the totally color blind there is always a marked diminu- 
tion of foveal acuity of vision, possibly because the differ- 
entiation of the retinal neuro-epithelium of the fovea has 
not evolved into the true cone type. 

It is an interesting observation that decreasing luminosity 
of the spectrum renders even a normal hexachromic relatively 
color insensitive, so that he sees the spectral colors gradually 
fade out into a thin gray band. This, however, is quite 
different from true color blindness in which there exists a 
physiological inability to apprehend light waves of certain 
periodicity no matter how high may be the illumination. 

It might be well in passing to call attention to the relative 
looseness with which color terms are applied. Probably 
one-half of a class will speak of the violet in a spectrum as 
purple, not through retinal misapprehension but because of 
inaccurate terminology. Many have but a vague notion as 
to what is the real difference between crimson and vermilion ; 
while the multiplicity of fanciful names applied to the newer 
aniline shades adds greatly to the general uncertainty. 

Test for Color Blindness.— The most widely used test for 
color blindness has been the Holmgren worsteds. This 
test consists of three standard large skeins of worsted— a 
pale pure green, a magneta, and a bright red; there are also 
a large number of tints and shades of each of the three 
samples, as well as a number of grays and browns. In using 
this test, the subject is given the green skein and then asked 
to select from the assorted mass all those of related color 


value; if the subject be both red and green bhnd, the test 
skem will appear to him either gray, bluish-gray, or yellowish- 
gray, and he will place with the sample all the greens, some 
of the grays, gray-yellows, and gray-blues. With the 
magenta test, the red blind wall place other purples, blues, 
and violets; but the green blind will select greens, grays, and 
lighter browns. With the red skein, the red blind will place 
with it all pure reds and pinks, grays, and the less luminous 
browns; while the green blind will choose other greens, 
grays, and the brighter browns. 

The Holmgren test has been rather sharply criticized. 
Based as it is on the Young-Helmholtz theory of color vision, 
it admits of but three types of color blindness— total, red, 
and green; whereas as Edridge-Green has shown, there may 
be four at least, with many possible minor variations. Then 
it is difficult to secure worsteds having saturated colors, 
or even two Holmgren tests of identical color values. The 
colors are liable to fade, and the skeins soon become so soiled 
as to affect their testing values; and it is claimed that a 
brown worsted has a different feel from a green one. Again 
the red-green color blind may be readily taught so he can 
easily pass the test; and finally, the test is too far removed 
from actual conditions in practice to be an efficient one, 
especially in the detection of red-shortened hexachomics. 

A more satisfactory test is either the lantern test, with a 
series of standards and confusions which the subject is re- 
quired to name; or the test with the movable diaphragm 
spectroscope where the subject is required to name mono- 
chromatic bands of light; or better still, one of these tests 
checked by the other. Any of these might well be supple- 
mented by a simple coloration test w^here the subject is re- 
quired to duplicate the coloring of a simple polychrome, 
when furnished a standard in black and white. 

The most satisfactory test for rapid investigation is the 
one devised by Ishihara. This test consists of a series of 
plates on each of which is printed a vast number of small 
discs of varying size and color. The arrangement of these 
colored discs is very clever. Shades, tints, and mixtures are 
so juxtaposed as to give a definite optical effect to the normal 


eye but a remarkably dissimilar effect to the color weak or 
color deficient eye. For example, in the test for red color 
vision, various red spots are so arranged that the normal 
eye sees some definite Arabic numerals standing out vividly 
in almost a has relief effect; but the red deficient eye sees, 
instead, different Arabic numerals, and does not see at all the 
numerals seen by the normal eye. In the test for green color 
vision, the normal eye sees two green numerals plainly; but 
the green deficient eye sees no numerals at all, because the 
various tints and varieties of green are so mixed up that any 
order is for the green color-blind undiscernible. Among the 
many other separatory tests is one where the red-green color 
blind see a contorted line which is invisible to the normal 


(a) Simultaneous.— It has been pointed out how any two 
colors separated spectrically by two intermediate colors, are 
complementary to each other giving white or gray if their 
spectral lights be blended. If any two such complementary 
colors, neither of which is terminal in the spectrum, be 
placed in juxtaposition, the effect on the eye is to alter the 
hue of each in the direction of the spectrum furthest away 
from the complement. For example, when orange and green- 
blue are placed in apposition, the hue of the orange inclines 
toward the red, while that of the green seems more bluish. 
If one terminal color be contrasted with a color proximal to 
the central green it seems to take on some hue of the other 
terminal; but if the contrasting color be distal to the central 
green, the terminal unit will not change in hue, but the 
contrasting color will appear to move somewhat toward 
the opposite terminal. When any of the colors are contrasted 
with gray, especially if the two be somewhat subdued by 
covering with thin tissue paper, the gray paper seems to 
take on somewhat the hue of the complementary of the color 
used; for example, if a piece of medium gray tissue paper be 
placed on a sheet of red, the gray tends to take on a bluish- 
green tinge. 


(b) Successive Contrast.— Retinal reaction does not cease 
immediately with withdrawal of the stimulus, but continues 
for a period whose length depends considerably on the dura- 
tion and intensity of the stimulus. With moderate intensity 
of the stimulus, but brief duration, the after-image induced 
in the retina is usually positive. With longer duration and 
identical intensity, the after image will usually be either 
negative or contrasted. In experimenting for after-images, 
one usually looks fixedly at the object (the primary) for a time 
then immediately shifts his eyes to a plane surface (the 
secondary) . When the primary and secondary are of identi- 
cal color there is, with colored lights, a gradual diminution 
of luminosity, with some slight shifting of hue toward that 
of lesser wave length. If the primary stimulus is white, 
and the secondary the same, there usually appears a black 
field corresponding in size and shape to the primary; this 
image may also have a chromatic corona. If the primary 
stimulus is colored, and the secondary is white, the after 
image is an exact counterpart in the color complementary 
to the primary, and has an intensity proportionate to the 
whiteness of the secondary. If the primary is colored, and 
the secondary is colored also but not identical, the after- 
image will be a hue matched by the complementary of the 
primary, and of the secondary, with the color of the comple- 
mentary predominating. 

The most plausible explanation of color contrast is that 
of primary inhibition followed by induced secondary action, 
analogous to the inhibition preceding the peristaltic wave in 
the intestines. This explanation assumes a very close rela- 
tion in the retina of the visual elements, expecially of those 
concerned with complementary color sensations. 


Since the fovea is the retinal area concerned with epicritic 
vision, it becomes essential that there be a mechanical 
adaptation of the eyeballs whereby the principal axis of 
vision of one eye shall be accurately coordinated with that of 


the other eye, and in such manner and degree that freedom 
of ocular movement shall permit of rapid adjustment of the 
line of sight upon the object of discrimination. 

The position of the eyeball in its capsule, with fatty tissue 
intervening, admits of great freedom, within restricted limits, 
of rotation on almost any axis passing through the center 
of the eye. These rotational movements are effected by the 
several extrinsic muscles of the eye, the muscles of the two 
eyes normally working together harmoniously to cause 
coordinated action. Rotation about the sagittal axis (or 
axis of vision) probably never takes place because of the 
oblique planes of force of the two oblique muscles. Rotation 
about the vertical axis is the most frequent movement; it 
takes place as the result of contraction of the lateral recti 
muscles, the outer muscle of one eye acting harmoniously 
with the inner muscle of the other eye in conjugate deviation, 
and the two inner muscles acting together when accommoda- 
tive efforts are indicated. Rotations about the transverse 
axis takes place whenever the eye moves up or down in one 
plane, and this is effected by the combined action of two 
muscles; the superior rectus moves the eye upward, its 
concurrent inward pull being balanced by the upward and 
outward rotational effect of the inferior oblique; conversely, 
downward rotation is effected by the inferior rectus, its con- 
current outward pull being balanced by the downward and 
inward pull of the superior oblique, with the lateral pull of the 
external rectus. Oblique movements are produced by the 
combined action of two recti muscles and an opposite oblique. 

The binocular movements of the eye are normally of but 
two kinds only : (a) The convergence of the visual axes which 
is always associated with accommodation for near objects, 
and is mainly effected by concurrent contractions of the two 
internal recti muscles; {h) Conjugate deviation with paral- 
lelism of the two visual axes, which is effected mainly by the 
external rectus of one eye acting concurrently with the 
internal rectus of the other eye. 

When the attention is directed toward a definite object, 
the simultaneous stimulation of the two retinae gives practic- 
ally a single sensation. When the attention drifts, as in 


day dreams, not infrequently the simultaneous stimulations 
give double sensations, one of which is usually more pro- 
nounced than the other. This indicates that the retinae 
possess what may be called "corresponding points" which 
are simultaneously stimulated whenever the principal line of 
vision from each eye extends to the same objective point. At 
the same time any object in this same line of vision, whether 
proximal or distal to the objective point, will stimulate non- 
corresponding portions of the retina, and will, therefore, give 
an additional separate sensation from each retina. The 
middle of the fovese constitute the centers of identical points; 
the remaining half of each retina is nearly identical with the 
corresponding half of the other retina, point for point, though 
corresponding points in the upper halves show a slight angular 
divergence from the vertical meridian. 

When two sensations are aroused as the result of stimula- 
tion of non-corresponding points in the retina, the weaker 
one is partially or totally inhibited. But experimentally, 
when a large number of non-corresponding points are simul- 
taneously stimulated, the attention of consciousness shifts 
from one to another, only one being held in attention at one 
time, the others being temporarily inhibited ; yet if there be a 
conscious relaxation of the ciliary muscle with no further 
attempt at focusing on either object, then both objects may 
be hazily perceived simultaneously in consciousness. When 
colored gelatin sheets are held before the eyes, the effect 
varies according to what is observed, and according to the 
condition of the ciliary muscle. For example, if a medium 
light green sheet is held before one eye, and a medium 
red-orange sheet before the other eye, attention may shift 
from one color to the other when the ciliary muscle is con- 
tracted, but a fusion may result if this muscle be relaxed. 
With such an arrangement of color sheets, the sky looks deep 
orange; a hemlock tree looks dark green, a white house looks 
white; a yellow flower looks white; now to show that an actual 
fusion takes place one compares the results to be obtained 
when he closes first one eye then the other, while looking 
at the above or other objects. But if now the attention be 
focused on some near point, there is liable to be a rapid shift- 


ing back and forth of the sensation in consciousness from the 
perception of one color to perception of the other. 

The explanation of corresponding points lies probably 
in the nerve supply. It is generally accepted that the nerve 
fibrils from the right hemisphere of the two retinae come 
together at the optic chiasm, and pass ultimately to the 
same side of the cortex where they terminate either in 
identical areas or in areas immediately adjacent. 


The impinging of a stimulus on any portion of the retina 
arouses in consciousness a sensation; this is referred to some 
external object lying along a straight line which in normal 
vision always extends from the stimulated spot through the 
nodal point to the object. This projection of the sensation 
to its radial source is a faculty acquired in early infancy in 
relation to muscle and tactile sensations; it is probably 
principally experiential for the individual, though, un- 
doubtedly, acquired racial inheritances may have a deter- 
mining influence during the early developmental stages. 
The connections of the retina with the cortex are probably 
such that about one-half of all impressions are contralateral. 

Judgments of Size, Distance and Solidity.— Several factors 
enter into judgments of this character. The size of the 
image on the retina is an important early factor as indicating 
the size of an object, it having been learned by many experi- 
ences that the apparent size of an object varies inversely 
according to distance (and there will be some variation in 
the extent of the stimulation of rods and cones) ; hence, the 
apparent size will influence one's judgment as to both the 
actual size and the distance. 

The estimation of the visual angle is much influenced 
also by those muscles having to do with focal adjustment. 
The nearer an object, which is within the far limit of vision, 
the stronger will be the contractions of both the ciliary, 
sphincter pupillse, and internal recti muscles; and it is quite 
probable that minute variations in the tensions of these 
muscles give definite, closely coordinated concepts in con- 


sciousness. Probably the most important factor is the mem- 
ory of previous experiences, wherein estimates of size and 
distance were mensurally verified ; so in any present estimate, 
apparent size and distance will be considered comparatively 
with earlier estimates. In many cases some known unit 
of estimate may be in the visual field contemporaneously, 
and will serve as a mensural criterion. 

Judgments of solidity are due to the fusion into a single 
concept of non-corresponding retinal sensations, and to 
variations in the accommodation effort as the eye follows 
retreating lines. Any solid that is not too distant must 
inevitably give non-corresponding impressions to the retinae; 
then, as attention shifts first to one detail and then another, 
with a following by the eye of receding lines, consciousness 
apprehends the mathematical perspective as that of an 
object having three dimensions. This power of judgment 
is very much inferior in monocular vision, and depends in 
large part on previous experience and judgments obtained 
with the use of both eyes. 

Sundry illusions readily arise in our visual experiences. 
Having once obtained a definite concept concerning the 
relationship between size and distance, consciousness persists 
in continuously so interpreting the sensation. For example, 
when a given object is so seemingly reduced in size as observed 
through the reversed opera glass, the diminished figure appears 
to have receded to a consistent distance. In a reverse 
manner, since distant objects seem somewhat hazy and 
have a rather uncertain outline, a near object with partial 
obscuration of outline seems much larger than it really is; 
as, for example, the sailing vessel coming suddenly out of 
the fog looms large on the immediate horizon. Also, any 
distant object, seen when the atmosphere is unusually 
clear and brilliant, seems smaller than normal because of 
the clear-cut outline. Judgments of solidity yield illusions 
whenever the interpretation of mathematical perspective 
admits of more than one choice. A great number of possible 
optical deceptions have been discovered; many of these are 
used as tests in the laboratory manuals of physiology. Some 
are of great historical interest, as having been instrumental 
in determining men's thoughts and theological conceptions. 


The eyeball receives its nutrition by means of a serous 
transudate from the ciliary capillaries. A very small part 
of this (2 per cent) passes back into the vitreous humor 
whence the excess is drained off through the lymphatics of 
the optic nerve. The major portion passes into the posterior 
chamber, thence through the pupil into the anterior chamber, 
from which the excess is drained off through the canals of 
Schlemm. It is estimated that an amount equal to 6 cmm. 
may be secreted a minute, and that this amount maintains 
intraocular pressure at about 25 mm. Hg. The intraocular 
pressure varies directly with the blood pressure, or with any 
influence affecting the rapidity of drainage. For example, 
inflammation blocking the spaces of Fontana dams back 
the intraocular fluid and promptly raises intraocular tension 
to a dangerous point; the chronic condition of this type is 
termed glaucoma. 

The portion of the globe of the eye exposed anteriorly 
is protected by the eyelids; these are lined by a membrane, 
the conjuctiva, which in turn is reflected over the front of 
the eyeball. The Meibomian glands, lying just beneath 
the tarsal conjunctiva, furnish a fatty secretion that serves 
to keep the edges of the eyelid oiled and thereby protected 
from tears; it also prevents adhesion of the lids during sleep. 

The conjunctiva is kept constantly bathed by the thin, 
watery secretion of the lachrymal gland. This secretion, 
which is normally being formed in small amounts as a reflex 
from the conjunctiva, is spread over the eyeball by the 
frequent winking of the lids, with the excess escaping down 
through the nasal duct. Any excessive production, as in 
emotional disturbances, may overflow the conjunctival 
chambei" and escape down the cheek. Tears are said to be 
weakly bactericidal. 


Cobb: Pupil Diameter and Visual Acuity, Am. Jour. Phys., 1914, 36, 335. 

Edridge-Green : Color Vision, Jour. Physiol., 1915, 49, 265. 
•, Edridge-Green: Simultaneous Color Contrast, Jour. Physiol., 1912, 43, 

Edridge-Green: Color Blindness and Color Perception, London. 


In all the higher multicellular animals there is a division 
of labor, with a consequent interdependence. The activities 
of all parts of the organism are dependent on the blood stream 
for renewals of the supply of food material and oxygen, and 
for the removal of waste. Normally this activity is modified 
by nervous influence and by the chemical condition of the 
blood. But it is solely through a modifying of the constitu- 
tion of the blood that the structures manufacturing internal 
secretions exert their influence on distant parts, an influence 
whereby arises a closer coordination of correlated activities. 

Whatever may be the nature of this chemical influence, 
identified in the cases of the adrenal secretion, anterior 
pituitary, and thyroid only, it is very active in extremely 
minute amounts. It is always derived from a definite sub- 
stance; and is always specific in action; it brings no additional 
energy to a given tissue, but seems to incite that tissue to 
renewed metabolic activity (hence the name hormone, from 
bpixavuv, to excite); it possesses no antigenic action, and is 
extremely labile in its activities being rapidly oxidized or 
otherwise destroyed by the tissues. 

It is feasible to group the internal secretions, in relation 
to their general activity, as nutritional, protective, and mor- 
phogenetic, somewhat after the plan proposed by Gley; 
such a grouping tends to make systematic discussion more 

Functional Table of Hormones. 

(r/) Nutritional. 

1. Pyloric (Fig. 7), influencing gastric secretion and 


2. Duodenal (Fig. 12), influencing hepatic, pancreatic, 
and intestinal activity. 

3. Pancreatic (Fig. 12), influencing glycophysis, especially 
by the muscles. 

4. Adrenal (Fig. 16), influencing glycogenolysis. 
(6) Protective. 

1. Liver (Fig. 14), influencing coagulability of the blood. 

2. Adrenal (Fig. 16), influencing the sympathetic auto- 

3. Parathyroids (Fig. 88), influencing detoxication of some 
katabolic products. 

(c) Morphogenetic. 

1. Thymus (Fig. 89), influencing genetic metabolism. 

2. Thyroid (Figs. 88 and 90), influencing osseous and 
neural metabolism. 

3. Pituitary or Hypophysis (Figs. 41, 43, 59 and 92), 
anterior lobe, influencing bone and connective tissue meta- 

Pituitary, pars intermedia, influencing unstriped muscle. 

4. Myometrium (or placenta?), influencing mammary 

5. Gonads (Figs. 93 and 94), influencing development of 
secondary sexual characteristics. 

(a) Nutritional.— The experiments of Edkins, as elsewhere 
discussed, indicate that a hormone is developed as a result of 
primary pyloric activity, producing a secondary stimulation 
of both the acid and the peptic cells of the stomach. This 
secretion is rapidly absorbed by the pyloric veins, and is 
carried by the blood stream to that portion of the stomach 
secreting gastric juice and there excites increased metabolism 
in the glandular structures. 

In the case of the duodenal secretion, a hormone is devel- 
oped as a result of the contact of the acid chyme on the 
duodenal mucosa. This secretin, absorbed by the blood, 
is carried to the pancreas where it excites the secretion of 
alkaline pancreatic juice. As soon as the pancreatic juice 
and the bile have neutralized the acid chyme, the formation 
of secretin ceases; but directly the sphincter pylori relaxes, 
a new lot of acid chyme enters the duodenum and starts the 



process anew. Related studies indicate that either this 
secretin, or another formed at the same point and time, 
has an exciting effect on both the secretion of bile and the 
secretion of succus entericus. 

Common carotid 

Right parathy- 

Inferior thyroid 

Remnant of laryn- 
geal nerve 

Fig. 88. — Parathyroid glands. (Halsted and Uvans.) 




Thy told veins 
Jiirjht vagvs 
Supenoi vena ca ia_ I 

Thij) Old [/land 

Left common 
caiotid artery 
Left internal 
jugvlar vein 

Left subclavian vessels 

Fig. 89. — The thjnui-- of a full-time fetus, exposed in situ. (Gray.) 

External carotid artery 

Superior thyroid artery 
Superior thyroid vein 

Vagus nerve 

Middle thyroid vein 

%. M 



The pancreas has other duties than that of forming the 
pancreatic digestive juice that escapes by the pancreatic 

Fig. 91.—^, a cretin, twenty-three months old. B, the same child, 
thirty-four months old, after administration of sheep's thyroids for eleven 
months. (Starling.) 

duct into the duodenum, there to act on proteins, carbohy- 
drates, and fats. Other portions of the pancreas have no 



connection with the radicles of the pancreatic duct, but are 
in intimate relation with thick capillary networks of blood 
vessels. These portions constitute the islands of Langerhans; 
they are not concerned with digestion, and remain unaffected 
when experimental interference has caused a complete 
atrophy of those pancreatic cells secreting digestive fluid. 

Fig. 92. — Mesial sagittal section through the pituitary body of an adult 
monkey (semi-diagrammatic), a, optic chiasma; 6, third ventricle; c, 
tongue-like process of pars intermedia; d, epithelial investment of posterior 
lobe; e, anterior lobe;/, epithelial cleft; g, pars intermedia; h, posterior lobe. 
(After Hering.) 

Experimenting on dogs it has been found that partial or 
complete extirpation of the pancreas is followed by those 
symptoms: polyuria ; glycosuria, extreme thirst, muscular 
weakness, emaciation, and ultimate coma— characteristic 
of diabetes in man. A number of observers have reported 
hyaline degeneration or atrophy of the islands of Langerhans 
in diabetes in man, though this does not appear to be a 



Tunica vagiruiUs 
Tunica albuginea 
Its septa 

Fig. 93. — Vertical section of the testis, to show the arrangement of the ducts. 

Fig. 94. — Section of the ovary: 1, Outer covering. 1'. Attached border. 
2. Central stroma. 3. Peripheral stroma. 4. Bloodvessels. 5. Graafian 
follicles in their earliest stage. 6, 7, 8. More advanced follicles. 9. An 
almost mature follicle. 9'. Follicle from which the ovum has escaped. 10. 
corpus luteum. (After Schron.) 


uniform appearance. But experiment and observation indi- 
cate that that portion of the pancreas represented by the 
islands of Langerhans has an exceedingly important function 
in connection with metabolism ; and the invariable appearance 
of glycosuria in diabetes, as in extirpation of the pancreas, 
indicates that this function is in relation to carbohydrate 

The Vienna school contends that pancreatic secretion 
and adrenal secretion are antagonistic in their effect on the 
glycogenolytic function of the liver, and that in absence of 
the pancreatic inhibitory secretion, the stimulating effect 
of adrenin results in excessive glycemia. This contention 
is seemingly disposed of by the fact that adrenin glycemia 
ceases as soon as the glycogenic power of the liver is 
exhausted, whereas pancreatic glycemia continues long after 
glycogen has disappeared from the liver. 

The theory that seems to be considered most favorably 
is that the islands of Langerhans secrete a hormone, termed 
insulin, which, to a considerable extent, influences the glyco- 
phytic activity of the muscle tissues. Absence of this 
hormone results in greatly diminished power of carbohydrate 
assimilation with the phenomena of hyperglycemia and 

Another activity having to do with the carbohydrate 
function is produced by adrenin, the principle secreted by the 
suprarenal glands. When adrenin is injected into the blood, 
there is an increase of sugar in both the blood and urine. 
If the adrenal nerve be stimulated, a like result ensues. A 
similar effect is also produced by emotional excitement, as 
well as by sensory stimulations of a protopathic t}^e. These 
several observations may be plausibly interpreted to indicate 
that adrenin, among other things, is a hormone which excites 
the liver to greater efforts at glycogenolysis, the apparent 
purpose being to render greater supplies of energy-yielding 
material more immediately available. Cannon's deductions 
are that this effect is protective to the animal either in flight 
or in combat, and is an invariable concomitant of those emo- 
tions aroused by a sense of the impending need for great 
muscular exertion. 


(b) Protective.— In discussing coagulability of the blood 
mention was made of fibrinogen and the hypothetical anti- 
thrombin. Experimental data indicate that both these 
substances are formed by the liver. The former substance 
serves for the formation of the fibrin in the blood clot, and 
is thus of great utility in protecting the organisms from the 
results of sanguinary encounters. Antithrombin, on the 
other hand, is assumed to serve the purpose of preventing 
intravascular clotting through keeping the prothrombin 
inactive; in this way it is an agent of immense utility in 
maintaining in a static condition forces of much dynamic 
potentiality. Accepting the findings of several investigators 
as to the hepatic origin of these two substances, a tentative 
conclusion may be hazarded that the liver provides a secre- 
tion that serves to inhibit one substance in the blood, and to 
activate another when certain conditions prevail. In this 
connection it may be recalled that adrenin in the blood also 
serves to accelerate the clotting process. 

Adrenin is a product of the suprarenal glands (Fig. 16). 
The most pronounced effect of adrenin seems to be a stimulant 
one on the receptor synapses at the terminations of the 
sympathetic portion of the autonomic system, producing 
contractions of myovascular tissue and relaxation of other 
smooth muscle, with acceleration of the heart; the resultant 
at any time being closely similar to that produced by stimula- 
tion of the sympathetic fibers. 

Adrenin can be isolated in an assumedly pure condition; 
and when administered the symptoms produced are practic- 
ally the same as are seen when stimulation is applied to the 
nerve supplying the adrenal gland. The principle, adrenin, 
is derived from the medulla of the adrenal gland solely, not 
from the cortical portion. 

Extirpation experiments with the adrenal gland are 
usually followed by fatal outcomes, except in those animals 
having an adequate supply elsewhere of chromaffin tissues, 
which also yield a pressor principle; from which it would seem 
that probably death is due to the loss of the medullary 
portion. Destruction of the adrenals by disease (Addison's 
disease) is accompanied by weakness, a lowering of blood- 


pressure, prostration, vomiting, and a peculiar bronzing of 
the skin (this last symptom at least is usually ascribed to the 
cortical involvement). 

These several data indicate adrenin to be a hormone acting 
in relation to smooth muscle in such a way as to maintain 
vascular tonicity, besides being related to carbohydrate 
metabolism and to blood coagulation. Some interrelation 
seems to exist also between the sexual organs and the adrenals, 
as indicated by the cortical hypertrophy that accompanies 

Parathyroids (Fig. 87).— Exact knowledge concerning 
the function of the parathyroids is very limited and labora- 
tory reports are conflicting. Perhaps the more-widely 
accepted findings are that when the parathyroids in the 
carnivora are completely removed the animal rapidly develops 
tetany tremors and convulsions and soon dies; whereas in 
some herbivora, like the rabbit, the chief symptom produced 
is a marked diminution in resistance. Many of the earlier 
fatal, or distressing, results attending the removal of the 
thyroids in human beings is now ascribed to the inclusion 
in the operation of some or all of the parathyroids. The 
symptoms brought on by removal of the parath\Toids, 
partial or complete, are as follows: Fibrillar contractions 
and tremors of muscle tissue, with spasmodic incoordinations 
attending all attempts to make voluntary movements; 
some of these symptoms may disappear when parathyroid 
substance is administered. There are also cases of tetany 
occurring in infancy or childhood, with an exhibition of 
similar symptoms; whence arises the idea that in tetany 
of infancy there is an insufficiency of parathyroid secretion. 
Tetany due to deprivation of the parathyroids may be much 
relieved by calcium administration. 

Although nothing in the case can be considered definitely 
settled, the view is propounded that the parathyroids secrete 
a hormone whose action is to neutralize some toxic substance, 
guanidin possibly, formed elsewhere in the body; in which 
case, deficiency of this protective substance would permit 
of an accumulation of the specific toxins in the body, with a 
detrimental effect upon the neuro-muscular apparatus 


(c) Morphogenetic— f/?6' Thymus Gland (Fig. 88).— The 
thymus gland probably exercises a profound though obscure 
influence on general metabolism. According to Howell, 
the gland retains its full size (and, hence presumably, its 
full function) until puberty, when it promptly begins a 
course of general atrophy. In some cases of arrested develop- 
ment in young people, the gland has been found persistent. 
Castration is followed by continued growth of the gland, while 
its removal is asserted to be followed by hastened sexual 
development, though other experimenters find that in young 
dogs removal of the thymus produces a retarded development 
resembling rickets, with increased excitability. Young tad- 
poles fed on thymus grow excessively, as tadpoles, with a 
considerable delay of the metamorphosis into the frog stage. 

The more generally accepted opinion is that the thymus 
gland is intimately connected with the physiology of growth 
during the prepubertal period, with possibly a repressive 
influence on sexual development. 

The Thyroid Gland (Figs. 87 and 89).— The thyroid gland 
has been the subject of extensive study, and the means of 
wonderful successes in treatment. It may be studied by 
means of the symptoms arising from: (a) Its absence in 
infancy; (6) its undue diminution later in life; (c) its adminis- 
tration to normal individuals; (d) its effect in hyperactivity; 
(e) its absence through surgical interference; (/) its use as a 

An infant having deficiency of thyroid remains stunted 
and undeveloped, ugly in appearance, idiotic in mentality; 
its osseous system remains infantile, its skin is heavy and 
thick; its abdomen, lips, and tongue protrude, it drools 
from the mouth, it develops a malformed skull; this condition 
is known as cretinism. If the infant receives no treatment 
it reaches adult age while remaining in size, appearance and 
mentality but a child of not more than two years of age. 
But let such a child be fed thyroid gland, or given thryoid- 
iodine, and mirabile dictu, in a few months the idiot becomes 
a bright, happy, well-formed child, necessarily somewhat 
handicapped by its years of retardation, but otherwise 
strong and normal (Fig. 91). 


Atrophy of the thyroid in adults, with a consequent marked 
diminution of its secretion, brings on the retrogressive 
condition known as inyxedema. The patient looks yellow 
and waxy; the face and hands become puffy and swollen 
through newly-formed subcutaneous connective tissue; 
the mental activities become blunted, cerebration is slow 
and faltering, and the speech is hesitant; the hair falls out, 
the intake of food is lessened, and the urea output is dimin- 
ished, with concurrent lowering of the temperature and 
lessening of the heart rate. Yet if to such an unfortunate 
subject, thyroid tissue, or thyroid-iodine, be administered, 
she recovers her mental and physical health, the swelling 
becomes reduced, and there ensues a new growth of hair. 

If thyroid be given in large doses to a normal individual, 
there ensues a marked increase in the katabolic processes 
of the body, the nitrogenous output exceeds the intake, the 
subcutaneous fat is rapidly oxidized and diminishes or 
disappears, the appetite increases, and the heart is accelerated 
even sometimes to violent palpitation (tachycardia) . 

Similar though more marked symptoms are seen when 
the thyroid is hyperactive, as in exophthalmic goiter. There 
ensues a progressive tachycardia with palpitation and 
breathlessness, muscular tremors with neurasthenia, vomiting, 
albuminuria, proptosis, increasing weakness and emaciation. 

Extirpation of the thyroid in children frequently produces a 
condition of tetany, and in adults a condition of myxedema. 
Experimental removal produces analogous results in monkeys. 
In carnivora, thyroidectomy (including the parathyroids) 
is followed by progressive tetany, accompanied by dyspnea, 
leading to death in about two weeks; in the herbivora, there 
is a progressive wasting accompanied with nutritional 
disorders. But these several extirpation results in animals 
may be prevented by a transplantation of some of the thyroid 
tissue, provided that the parathyroids are left intact. 

These many facts lead one to the conclusion that the 
thyroid manufactures a hormone which exerts a profound 
influence on the metabolism of all the tissues of the body. 
When this secretion is deficient in infancy, anabolism is 
inadequate for more than maintaining the status quo; when 



it is deficient in adults, the retrogressive changes develop 
more rapidly than normally; when it is present in excess, 
katabolism exceeds anabolism, and the presence in the blood 
stream of immature or alien products brings on a progressive 
toxemia. Thyroid secretion is apparently a substance of 
great influence on metabolism. 

What the exact nature of this hormone may be is uncer- 
tain but recent investigations by Kendall show the presence 
of a crystalline compound containing 60 per cent iodine; 
Kendall finds administration of this iodine compound equal in 
effectiveness to the powdered gland in the treatment of 

The Pitvithry Body or Hypophysis (Fig. 91).— Our infor- 
mation concerning the function of the hypophysis is not 
conclusive, but some of the clinical and experimental data 
yield suggestive results. Complete removal of the hypophy- 
sis, or of the anterior lobe, is rapidly fatal; removal of the 
posterior lobe, including the pars intermedia, is follow^ed by 
sexual unrest, a tendency to obesity, and an increased toler- 
ance for carbohydrate food. 

Administration of the extract of the pituitary body yields 
conflicting results, as might be expected from so uncertain 
a protein substance; but certain generalizations may be 
tentatively submitted. Extracts of the anterior lobe, or of 
the posterior lobe, yield no results; but extracts of the 
intermediate portion produces a slowing of the heart with 
increase in blood-pressure, stimulation of most of the smooth 
muscle of the body, and possibly a stimulation of some of the 
glandular tissues. 

Tumors of the pituitary body (presumably of the anterior 
lobe) occurring during the period of growth, result in a great 
increase in the development of the long bones, producing 
''gigantism." A tumor of the pituitary body in an adult 
produces the condition known as acromegaly, where there is 
renewed growth of the bones of the face, hands, and feet; 
headache, polyuria, and ocular disturbances. These con- 
siderations appear to indicate that the anterior lobe secretes 
a hormone which has a marked effect on metabolism, especi- 
ally of bony and connective tissues; while the pars intermedia 


furnishes a hormone that has a stimulating effect on unstriped 

Mammary Gland. — Concerning the possibility of a hormone 
acting on the mammary gland very little may be said con- 
clusively. It is known that the glandular tissue of the 
mammae exhibit growth and extension as an early sequence 
of pregnancy; and as this takes place independently of neural 
connection, it is assumed that some substance of a hormone 
nature arises, in connection with endo-uterine changes, that 
stimulates the growth of the lactogenic apparatus. But 
whether this stimulus arises from the myometrium, the 
placenta, or the fetus, is not definitely known, the experi- 
mental data being conflicting. Some earlier experiments 
seemed to indicate a possible causal relationship of the corpus 
luteum, but these findings have not been confirmed. This 
action on the mammary gland is morphogenic but not 
secretogogue. Secretion does not ordinarily take place 
until after parturition; and it is customarily supposed that 
secretion is held in check by some inhibiting body belonging 
to the so-called chalone group; but this assumption is highly 

The Gonads (Figs. 92 and 93).— It has been known from 
ancient times that the removal of the germ glands in either 
sex prevented entirely the development of the secondary 
sexual characteristics; in fact, tended to bring on a neuter 
condition in which the victim approximated an indeter- 
minate condition unlike the normal of either sex. Some 
distressing results in the earlier history of gynecological 
surgery, in which there was performed a total oophorectomy 
with a consequent production of an artificial menopause, 
indicated a similar controlling influence by the gonads on 
the retention of the definite secondary sexual characteristics. 
Females, thus early deprived of their germ glands, tended 
rather rapidly toward a neuter condition in both mental 
and physical attributes; later, it was discovered that these 
lamentable deviations could be prevented by the successful 
transplantation of ovarian tissue, or even to a less extent by 
the administration of ovarian extract. At the normal 
menopause, retrogressive changes seem to be normal; how 


much these might be obviated experimentally is yet to be 

When a young castrated male animal is supplied with a 
transplanted testicle, the animal will develop complete 
male characteristics. Later, if the transplanted gonad be 
examined, the spermogenic elements will be found to have 
disappeared, while the interstitial tissue will have increased 
in size. If a young castrated male guinea-pig be furnished 
with a transplant of a female gonad of the same species, then 
this male animal develops secondary female characteristics. 

All this data indicates that the gonads exercise a pro- 
found morphogenetic influence on those physical and mental 
qualities especially concerned with the continuance of the 
species; and that this influence is presumably due to a hor- 
mone secreted by the interstitial cells of the gonad, and not 
by the reproductive cells. 

There also seems to be some occult influence exercised 
by the gonads on general metabolism. In mature animals, 
castration or spaying, is followed by renewed activity and 
growth of the thymus gland. Then, too, castration brings 
on an increase in size of the adrenals, though these glands in 
the female show a diminution in size following spaying. 
What may underlie these interrelations is nor known, though 
it is assumed they are due to some intimate autacoid influence. 


Internal Secretions : 

Shaffer: The Endocrine Organs, 1916. 

Marshall and Jolly: Transplantation of the Ovaries, Quart. Jour. Exp. 
Phys., 1908, 1, 115. 

Oliver: Internal Secretion of the Ovary, Jour. Phys., 1912, 44, 355. 

McCrudden: Effect of Castration on Metabolism, Jour. Biol. Chem., 
1909, 7, 185. 

Paton: Relation of Thymus and Sexual Organs, Jour. Phys., 1911, 42, 

Koch: Physiology of Parathyroid, Jour. Lab. Clin. Med., 1916, 1, 299. 

Vincent and Jolly: Functions of Thyroid and Parathyroid, Jour. Phys., 
1906, 34, 295. 

Tatum: Experimental Cretinism, Jour. Exp. Med., 1913, 17, 636. 

Cunningham: Experimental Thyroidism, Jour. Exp. Med., 1898, 3, 417. 

Hesselberg: Thyroid Grafts in Guinea-pig, Jour. Exp. Med., 1915, 21, 

Auor and Gates: Suprarenal Action, Jour. Exp. Mod., 1917, 16, 201, 


Bell, Blair: Experimental Operations on the Pituitary, Quart. Jour. 
Exp. Phys., 1917, 11, 77. 

Fenger: Composition and Activity of Pituitary, Jour. Biol. Chem., 1916, 
25, 417. 

Lusk: Physiology of the Thyroid, Jour. Am. Med. Assn., 1924, 83, 15, 

Hooker: Physiology of the Suprarenal Glands, Jour. Am. Med. Assn., 
1924, 83, 18, 1430. 

Howell: Physiology of the Pituitary Gland, Jour. Am. Med. Assn., 1924, 
83, 21, 1684. 

MacCallum: Physiology of the Parathyroids, Jour. Am. Med. Assn., 
1924, 83, 23, 1846. 

Carlson: Physiology of the Ovaries, Jour, Am. Med. Assn., 1924, 83, 
24, 1920. 


In Nature, the dominant sine qua non is the perpetuation 
of life; all other functions serve this end ultimately. Of all 
the cells of the living organism the germ plasm only is immor- 
tal. It is handed on from life to life, that medium being 
used which is seemingly most fit to survive all the storms 
and stress of existence. 

For maintaining the continuity of life certain conditions 
are essential. (1) The parent organism must adequately 
protect the germ plasm. (2) Opportunity must be afforded 
for the escape of germ cells from the enveloping stroma. 
(3) There must be cross-fertilization to ensure a continuance 
of maximum vitality. (4) A new life-union having been 
initiated, it must be securely nurtured during embryogenesis ; 
and then, (5) Having acquired the racial morphology, it 
must be nurtured and assisted to reach the stage where it 
is prepared of itself to pass on the germ plasm anew. Look 
where we will among the higher metazoa, in the animal or 
vegetable world, we find these several conditions provided 
for. Vast numbers of potential beings fail to reach the higher 
phases; but, in the prodigality of Nature, usually enough 
survive to ensure a continuance of the life cycle. 

In the lower forms, reproduction takes place through a 
long series by means of binary division, though it is not 
unlikely that ultimately Avith all these forms there is a term 
of fusion conjugation, whereby chromosomic vitality is 
renewed. In all except the very lowest organisms, cross- 
fertilization is a characteristic prerequisite of development. 

With the progress of evolution, with its constant special- 
ization of cells or cell-groups for particular purposes, in time 
there arose a group of cells specialized for the sole purpose of 


guarding the germ plasm; and at about the same time there 
developed a differentiation of the parent .stock into two 
marked t}^es, the male and the female. In this separation 
into type, the special function of the male came to be the 
furnishing to the egg cell new groups of chromosomes; the 
special function of the female became that of furnishing 
protection and nourishment to the new life until its develop- 
ment had reached the phylogenetic stage. This specializa- 
tion of organic function into male and female types can be 
traced biologically far down the phylogenal tree, in both the 
animal and vegetable kingdoms. 

The mechanical means for securing cross-fertilization 
varies considerably in different forms. In the lower herma- 
phroditic forms, the male gametes, formed in one part of 
the organism, travel a greater or less distance to meet the 
female gamete formed in some other portion of the animal's 
body. In higher t^^es there is an external fertilization, as 
among most fishes where the silt is deposited over the eggs 
recently laid by the female. In the higher vertebrates, 
where exists greater need for protection, and a relatively 
lower viability of the sperm, the method of cross-fertilization 
is of the internal type. In all the higher vertebrates the 
structures adapted for internal fertilization are similar; 
and the terminology of the facts of reproduction are identical 
throughout all Biology. 

In the process of reproduction certain structures, the 
gonads, are fundamental, inasmuch as these are the special- 
ized bearers of the germ plasm. Accessory to the gonads 
are other structures, specialized according to sex. In the 
male there are the vas deferens, for conveying the fertilizing 
fluid onward from the gonad ; a tubular structure for ensuring 
seminal deposition well within the body of the female; and 
some lesser structures: the vesiculce seminales, for storing 
excess of testicular secretion, and the prostate and Cowper's 
glands for furnishing diluents and solvents. In the female, 
there are the oviducts, for conveying the germ cell from the 
gonads to the gestation sac; the uterus, where the new life 
grows into the matured form; and the vagina, serving as an 
avenue of communication between the gestation sac and 


the external world. Another important accessory structure 
in the female is the mammary gland, which serves through its 
secretion to nourish the new life during the first few months 
of extra-uterine existence. 

Maturity.— Developmental changes of far-reaching influ- 
ence take place in both sexes about the fourteenth year, not 
infrequently a year earlier in females; the reproductive 
organs begin to assume the mature form and condition, 
and the various secondary sexual characteristics make their 
appearance. But though the generative organs may become 
functionable at the age of fifteen, and viable spermatozoa 
may appear at the age of sixteen, yet there remains a physical 
and mental immaturity that makes exercise of the repro- 
ductive function at this age not for the best interests of 
the individual or of society. As social evolution proceeds, 
more and more the genesic instinct becomes subordinated 
to altruistic considerations; and the profligate polygamous 
actions of those on a relatively-lower evolutionary level give 
way to that higher self-control that seeks a creative expres- 
sion in humanitarian activities. 

In some cases strange genesic strivings appear for a short 
time in childhood; these manifestations require great patience 
and tact for their safe and successful repression. G. Stanley 
Hall thought these disturbances might be considered rever- 
berations in the soul of a long-distant past when sexual 
maturity was attained at a much earlier period of life than 

Menstruation.— In the female, one of the first manifesta- 
tions of approaching maturity is the appearance of the 
menstrual flow. This consists of a periodic discharge from 
the uterus of a mixture of endometrial and cervical detritus 
in a vehicle of mucous, serum, and blood. This flow amounts 
to about 200 grammes, continues from three to five days, and 
is accompanied by considerable malaise, with possible 
nervous and digestive disturbances. 

What may be the significance of the menstrual flow is 

a debated question. That it has a definite and important 

relation to ovulation is shown by its complete cessation when 

the ovaries have ceased their function; but Avhether it pre- 



cedes ovulation, or succeeds it, is not definitely known. 
Those who think that menstruation precedes ovulation, as 
the precestrum in dogs precedes fertilization, view^ the 
endometrial exfoliation as a preparation for the reception of 
the ovum. Those who view ovulation as the earlier phe- 
nomenon think the menstrual process to be an endometrial 
dismantling of a structure originally prepared for the recep- 
tion of an ovum but now discarded on the failure of the 
ovum to be fertilized, without which fertilization the ovum 
is unable to effect a lodgment. 

Ovulation (Fig. 93).— Ovulation is the process whereby an 
ovum escapes from the stroma of the ovary. It has been 
stated that the ovary contains originally about 70,000 
potential ova, one of which is supposed to ripen every lunar 
month from the time of puberty until the arrival of the cli- 
materic. The ripening of the ovum consists of its extended 
development within the Graafian follicle, including matura- 
tion (see below) and the extrusion of the egg from the ovarian 
tissue. The mechanism of this extrusion is not understood, 
but may be due to a relative increase of adjacent vascular 
pressure. When once the ovum has escaped, the remaining 
follicle becomes filled with a blood clot which, in turn, rapidly 
becomes invaded with lutein cells, forming the corpus 
luteum. This physico-histological change continues for 
between two and three weeks unless impregnation ensues, 
in w^hich latter case the corpus gradually increases in size 
until the end of pregnancy. Some writers consider the corpus 
luteum of pregnancy possessed of a secretory power having 
an inhibitory influence on ovulation during pregnancy, but 
the nature of this assumed inhibition, or its extent, is 

Maturation of the Ovum.— Before the ovum escapes from 
its stroma, or soon thereafter, it passes through a reduction 
process whereby one half the number of chromosomes char- 
acteristic of that sex and species are extruded from the egg 
as the two polar bodies, and become lost (Figs. 95 and 96). 
Thus, the ovum becomes prepared for a cross-union whereby, 
from another source, a spermatozoon, there is supplied a 
quantity of chromosomes equal to what has been lost; 




thus there may be estabhshed an entirely original cell 
containing two sets of chromosomes, one bearing maternal 
characteristics, and the other set bearing the characteristics 
peculiar to the paternal side. 

From embryological studies it is learned that a similar 
reduction of the chromosomes occurs in the development of 
the spermatozoa so that each spermatozoon (Fig. 97) pos- 
sesses but one-half the number of chromosomes normal 


Fig. 95. — Formation of polar bodies in asterias glacialis. (Slightly 
modified from Hertwig.) In I the polar spindle (sp) has advanced to the 
surface of the egg. In II a small elevation (p6^) is formed which receives 
half of the spindle. In III the elevation is constricted off, formirig the first 
polar body {pb^), and a second spindle is formed. In IV is seen a second 
elevation which in V has been constricted off as the second polar body {ph"^) . 
Out of the remainder of the spindle (/.pn in VI) the female pronucleus is 

for the cells of that sex and species (Fig. 98). Therefore, the 
union of the ovum and sperm cell results in the formation 
of a new cell having the requisite number of chromosomes 
typical of the cells of that species. 

Union of the male and female germ cells may take place 
at any point above the cervical canal, but physiologists 
usually assume that the meeting point is somewhere within 
the Fallopian tube, and perhaps most usually near the 



fimbriated extremity. The ovum enters the ostium abdomi- 
nale, and is carried toward the uterus by the cihated cells 
in the lumen of the tube. The spermatozoa, by their own 
tadpole-like movements, make their way from the environs 
of the cervix, up through the cervical canal, over the endo- 
metrium, and into the tube. Except as their course may be 

Primary oocyte 

Primary oocyte 


O First 'polar 

ovum \ ] 

Polar bodies 

Fig. 96. — Diagram showing the reduction in number of the chromosomes in 
the process of maturation of the ovum. 

uncertainly determined by a chemotropism, the attaining 
of the entrance of the tube by any spermatozoon must be 
largely through mere chance. To more surely give proba- 
bility to that chance, the number of spermatozoa available 
at any one time amounts to millions; from so vast a number 
one, at least, may be reasonably expected to attain the goal. 



One spermatozoon only is adequate for fertilization of 
the ovum; and when that one has secured its entrance, 


Connecting piece 




/ Head-cap 


Anterior centriole 
Posterior centriole 

Spiral thread 
Mitochondria sheath 

Terminal disc 
Axial filament 

A B C 

Fig. 97. — Human spermatozoon. Diagrammatic. A. Surface view. B. 
Profile view. In C the head, neck, and connecting piece are more highly 

none other is able to effect a union with the already fertilized 
cell, perhaps because of the immediate reflex establishment 



of III! impermeable peri()^'lllal• film. Having entered the 
cytoplasm of the ovum, t\v^ two nuclei approach each other 
and fuse into one (Fig. 99); just before fusion takes place, 
the male kinosome separates from the pronucleus, and appar- 
ently soon takes up its work of energizing the new nucleus 
to an early resumption of karyokinesis. Soon the infinite 
processes of cleavage (Figs. 100 and 101), reduplication, 
and specialization commence; the ovum, in the meanwhile, 
traveling down the tube to find lodgment on the soft, 
vascularized endometrium. As it approaches the destined 

Primary oocyte 

Secondary f \ 
oocyte \ J 

Mature f^\ 


() o o o O O O O 

Polar bodies 


Fig. 98. — Scheme showing analogies in the process of maturation of the 
ovum and the development of the spermatid (young spermatozoa.) 

spot, numerous digitations appear on its surface and seem 
to provide it with an adhesive power for attaching itself 
to the uterine mucosa. Thence ensues that long, complicated 
process of development wherein and whereby a unicellular 
organism becomes transformed into a human being. 

Nourishment of the Embryo.— Unlike the ova of some lower 
forms, the human ovum contains very little nourishment for 
its sustenance; this amount sufficies until the ovum becomes 
attached, by means of the villi of the chorion, to the uterine 
mucosa, when it begins to gain sustenance by means of 



absorption from the uterine lynipli. Later, as arise f^reater 
needs, the chorionic villi penetrate more deeply, and ulti- 
mately come into relation with the vascular sinuses of the 
uterus; at the same time, bloodvessels from the embryo 

1. Polar hod 
Female pronucleus 

Male 'pronucleus 


Female pronucleus 
Male pronucleus 




Female pronuclei 

r. ',j~Male p)ronucleus 


Fused pronuclei 




Fig. 99. — The process of fertilization in the ovum of a mouse. (After 


proceed into the villi so that finally the blood of the mother 
is separated from the blood of the embryo by a thin endo- 
thelial wall only, and through this membrane food materials 
can pass in ample abundance. There is no actual mingling 
of fetal and maternal blood, but through the intervening 



membrane anabolic material passes from the mother into 
the blood stream of the child, and in the reverse direction 
are passing limited amounts of katabolic material from 
the rapidly-growing embryo. As Howell well says: "The 
nutrition of the fetal tissues is maintained in much the same 
way as though it were an actual part of the maternal organ- 
ism." Very early there seems to be a need for all those 

Fig. 100. — First stages of segmentation of a mammalian ovum. Semi- 
diagrammatic. (From a drawing by Allan Thomson.) z.p. Zona striata. Polar bodies, a. Two-cell stage, h. Four-cell stage, c. Eight-cell 
stage, d, e. Morula stage. 

constructive proximate principles essential at any time for 
the maintenance of life; but just how these principles pass 
from the mother's tissues into the placental blood stream, 
whether by diffusion, osmosis, or by selective cellular activity, 
is unknown; possibly all three factors may be utilized. 
Throughout the earlier stages of embryonic . development 
the maternal organism performs all the metabolic activities 



essential for life, but gradually the embryo develops various 
functional capacities, which, though not exercised much 
until birth, become ready for their extra-uterine activities 
when the great change comes. 


Fig. 101. — Diagrams showing the segmentation of the mammaHan ovum 
and the formation of the blastodermic vesicle. (Allan Thomson, after van 

Physiology of Parturition.— Little that is conclusive is 
known concerning the physiology of parturition. It is 
known that uterine contractions take place with a certain 
monthly regularity during the period of pregnancy; and that 
as pregnancy advances the force of the contractions gradually 


iiKTctiscs, cind sonietiiiics, in the predisposed, may bring 
on a misearriage in the eighth or ninth lunar month; but 
what gives to these contractions their final efficiency is uncer- 
tain. Some writers would ascribe it to degenerative changes 
taking place in the placenta, others to assumed increasing 
venosity of the blood, others to a reflex arising from the 
mechanical distension of the uterus; yet another thinks the 
mammary glands may at this time secrete a hormone whose 
effect is to stimulate the smooth muscle of the uterus to 
forceful contraction. It has been observed that various 
reflex disturbances of the sympathetic system (fright, for 
example) have at times been adequate for initiating uterine 

In parturition the strength of these contractions gradually 
increases both in intensity and frequency until in about 
ten hours the cervix has been sufficiently dilated to permit 
continued contractions to force out the living contents of the 
uterus. The placenta follows the child in from ten to forty 

The Function of the Mammary Gland.— Mention has already 
been made of the connective tissue changes taking place in 
the mammary gland at puberty. With the advent of preg- 
nancy a second change appears in the development of the 
alveoli of the secreting tubules, though very little glandular 
activity is at this time present. With the uterine changes 
attendant on parturition, a third phenomenon arises; the 
secreting alveoli become markedly active, producing for the 
first few days a thin, highly albuminous secretion, bearing 
a considerable amount of colostrum; but soon the secretion 
shows a markedly higher percentage of both fats and sugar. 

The act of nursing stimulates the glands to renewed 
activity, while cessation of nursing will result in retrogressive 
changes with functional atrophy of the tubules. A second 
conception arising during the period of lactation soon alters 
the secretion and causes it to diminish and finally cease. 
Removal of the ovaries brings on a secondary atrophy of the 
mammae. Sharp stimulation of the sympathetic system, 
whether sensory or emotional in its source, alters the constitu- 
tion of the secretion, and may even effect its entire cessation. 


But just what may he tlie real mechanism of milk secretion 
is a problem for future solution. 


The secondary sexual characteristics developed in the 
male at puberty are : Increased sense of mental and physical 
power; rapid increase in growth; the appearance of a special 
functional capacity in the generative organs; initiation of 
growths of hair on the face, chest, and pubes; deepening of 
the voice. For the next few years the boy usually growls at 
a more rapid rate than formerly. 

With the attainment of fuller maturity great quantities 
of spermatozoa are formed in the testes, and crowed the 
vas deferens and vesiculcs seminales; this functional activity 
is aggravated by local congestions, sensory irritations, or 
correlated emotions or imaginings. Spermatozoa are normally 
formed far in excess of monogamous needs, possibly as a 
survival of primitive polygamous conditions. Not infre- 
quently the excess may be spontaneously expelled; but it is 
not unlikely that not much excess would be produced, or 
if but slowly produced would be reabsorbed, if the male 
were early taught the mental and moral value of conservation. 

The utilization of the generative organs for the function 
of reproduction involves a special adaptation of the structures 
concerned for the destined purpose. Sensory impressions 
acting afferently through the pudic nerve, or related emotions 
acting through the cranio-spinal autonomics, cause the vesi- 
culse to contract vigorously, thereby forcing the contents, 
the massed spermatozoa, into the urethra, and the combined 
secretions constituting the semen are then forcibly expelled. 

In the material thus expelled exist thousands of possibili- 
ties for the transmission of paternal and patro-ancestral 
traits and characteristics to a new life vibrant with great 
potentialities. Yet of these thousands, only one cell group 
is normally successful in uniting itself with the female 
pronucleus. But from this union arises that marvelous 
product of evolutionary development— a human being. 
What shall be the mental, physical, and moral endowment 


of that new life? ''Do men gather grapes from thorns, 
or figs from thistles?" Yet a Burbank applies selective 
insight, and finally from a worthless cactus is developed a 
valuable production; what fundamental physiological factors 
may not be utilized for attaining equally remarkable results 
in the production of a race of super-humans! 

The Determination of Sex.— History records many and 
various, as well as vagarious, theories to account for the 
determination of sex; but a majority of these cases are 
supported by careful observation of those instances that 
seem to prove the opinion, and further buttressed by a 
studious ignoring of an equal number of cases that contradict 
the rule. The view most widely held at present is that sex 
is a Mendelian character, dependent on the presence or 
absence of an hereditary unit; when this unit is present, 
the zygote is female, but when it is absent, a male develops. 
The experimental data indicating this conclusion consist 
in part in the observation that in many animals, including 
man, about one-half of the spermatozoa contain an odd 
number of chromosomes, but all ova contain an even number; 
and many experiments indicate that the gender of the new 
zygote will depend on whether or no the odd gamete is the 
fecundating factor. If the zygote possesses an even number 
of chromosomes, the resulting embryo will be male; but it 
will be female if the zygote possesses an odd number of 


Guthrie: Influence on Offspring of Ovarian Engraft, Science, 1911, 33, 

Pearl and Surface: Action on Uterus of Glandular Extracts, Jour. Biol. 
Chem., 1914, 19, 263. 

Marshall and Runciman: Ovary and (Estrus, Jour. Phys., 1914, 49, 17. 


The history of the ''Jukes" family shows a vast number 
of criminals^ paupers, and harlots descended from a single 
pair of social renegades. Occasionally in this line of dis- 
repute there appeared an individual superior to the others; 
but intermarriage with one bearing the degenerate stigma 
resulted in a family no better than the average. 

The history of the descendants of two English immigrants 
to Connecticut, Elizabeth Tuttle and Richard Edwards, 
discloses a long line of prominent educators and college 
presidents ; yet from the union of this same Richard Edwards 
with his second wife, there descended nothing but mediocrity. 

Into the Virginia colony, composed largely of the flotsam 
of English society, came the Randolphs and the Lees; and 
from the union of these two families has descended a long 
illustrious line of statesmen and military leaders. 

Wherein resides that force, and of what does it consist, 
that yields educators from one group, statesmen from another, 
and criminals from a third? Or, to make the problem more 
fundamental, what is that which gives specific direction to 
morphogenesis, so that from undifferentiable cells there may 
arise a salamander, a fish, a bovine, or a human being? 
And what is that which gives tallness to one person, and 
shortness to another, blue eyes to this individual and brown 
eyes to another, qualities of leadership to a Lee and of way- 
wardness to a Juke? And are there determinable laws that 
are utilizable in perfecting the vital fabric? 

The balancing of hypotheses, and the outcome of infinite 
experimentation have gradually pushed back the assignable 
factors into the primitive pronucleus of the germ plasm. And 
within the nucleus have been found bodies to which is 


assigned the responsibility of being the bearers of heredity; 
these bodies are the chromosomes (Fig. 1). At the ovum's 
period of maturation, the maternal chromosomes become 
reduced in number to one-half that characteristic of the 
species; this ovum, if destined for fertilization, later meets 
a spermatozoon whose chromosomes have been similarly 
reduced; the union of these two starts a new life which will 
later show characteristics, both physical and mental, akin 
to those peculiar to both of the parents and to their respec- 
tive ancestors. Wherein lies the explanation? 


The first great theory of heredity was that of Lamarck. 
His theory contended that environmental conditions are 
constantly producing adaptive modifications whereby the 
individual becomes better fitted to meet the various exi- 
gencies of existence; and that these acquired characteristics 
of the individual are reflected in his chromosomes, and so 
passed on down as inherited characteristics. 

Darwin's natural selection theory assumes a constant 
slight fluctuation from generation to generation whereby 
the offspring varies in minute details from the parent, and 
that such variations will persist as are of value to the possessor 
in the struggle for existence. The effective factor in pro- 
ducing these fluctuations is unaccounted for; but it is assumed 
that each such variation is registered, together with the 
characteristics of every cell, by gemmule-representatives 
in the chromosomes; so the chromosomes, as the bearers 
of heredity, have in them infinitesmal representatives of all 
cells at all stages of existence. This has been termed the 
theory of Pangenesis. 

The theory of Weissman contends for the priority and per- 
sistence of the germ-plasm from which is derived all body- 
plasm with its sequent ofl^spring germ-plasm and involved 
body-plasm. This idea necessarily predicates a conception 
of germ-plasm in which must abide definite factors deter- 
mining both germ and somatic development along definite 
phylogenal lines. Thus, in the human ovum, there must 


be contained definite "determinants" which carry the embryo 
through and by all earlier phylogenal forms up to the human 
form, with all of its marvelous differentiations and special- 
izations; and these factors must direct not only all the phases 
of specific development, but must also endow the new germ- 
plasm with determinants of a like order. In the Weissman 
theory, variation is wrought by permutations of an infinite 
possibility of variety; these permutations are brought about 
through the elimination of certain combinations at the time 
of the reduction of the chromosomes, and a secondary rea- 
lignment ensuing from the new union of modified male and 
female pronuclei. Thus in each generation there is a new 
recombination of various ancestral germ-plasms, each with 
its own peculiar determinants; and the new combination 
cannot possibly be just like its ancestor, though it has a 
reduplicable racial kinship. Gradually some determinants 
may be lost or suppressed, while others will persist and ascend 
in relative dominancy. 

In this theory environment plays little or no part in the 
control of heredity, except as variations in parental nour- 
ishment may affect the relative vitality of the germ-plasm; 
in the germ-plasm reside each and all determining factors, 
above which the body cannot rise and from whose influence 
it is impossible to escape. Education cannot alter the con- 
stitution of the endowment, though it can render more 
eftective all utilizations of that endowment. The influence 
of this theory on all speculations along this line has been 
very great. 

Reasoning more from the experimental side, de Vries 
claims variations arise suddenly by the appearance of new 
and strange combinations, formerly called "sports." This 
mode of development, by means of sudden variants instead 
of through a prolonged summation of minute variations, 
constitutes the method known as the mutation theory. 

Closely related to the above theory, though having much 
that is akin to the fundamental proposition of Weissman, 
is the law of Mendelian inheritance. In the Mendelian 
theory, in place of Weissman's determinants, there are 
assumed to be "unit characters,' the idea' being that any 


mental or physical trait or characteristic of an ancestor is to 
be considered a separate unit, there being, of course, as many 
units as there are possible characteristics. In this theory, 
it is further postulated that each parent hands on to the 
offspring a complete set of unit characters, so that complete 
representatives from each parent are present in each chro- 
mosomic unit. Sometimes these units seem to blend, as in 
the skin color in the cross between an Ethiopian and a Cauca- 
sian. In other cases, instead of blending, there is a coex- 
isting of the unit characters; in such circumstances, one of 
the units, termed the "dominant" will be manifest while 
the other, termed the "recessive," will not be apparent in 
the present generation though it may appear at some later 
generation, at which time it becomes a dominant. 

It is a common observation that the children of any one 
family show individual variations from their parents and 
from each other. From this and many other analogous 
observations, it is assumed that there is not a uniformity 
in the distribution of unit characters among the gametes. 
Each gamete, whether male or female, possesses an indi- 
viduality; and while all have the broad, fundamental unit 
characters typical of the branch, yet each does not have 
universal representation of the more recently evolved units. 
For example, a blue-eyed person has all the unit characters 
of racial significance, but is lacking that particular character 
that determines pigment deposition in the iris. Now, if a 
male gamete so constituted should unite with a female gamete 
similarly restricted, the resulting zygote will be one in whom 
pigment absence from the iris is itself a dominant character- 
istic, and the resulting child will be a pure blue-eyed. But if 
this pure blue-eyed person mates with a pure brown-eyed, 
then all the offspring of this second generation will be brown- 
eyed, inasmuch as iris pigmentation is a dominant charac- 
teristic, whereas absence of pigmentation is a recessive char- 
acteristic. Assuming now that a child of this union should 
mate with a child likewise descended from the union of a 
pure blue with a pure brown, then there will arise four possi- 
ble permutations. A male pure-blue gamete may unite 
with a female pure-blue, in which the result would be a 


segregated pure-blue zygote; or a male brown may unite with 
a female brown producing a segregated pure brown; or a 
blue male might unite with a brown female, or a brown male 
with a blue female, in either of which cases there would result 
a hybrid having brown dominant and blue recessive. Thus 
the union of a hybrid, having dominant brown with recessive 
blue, with another hybrid similarly constituted, will produce 
in the proportion of one pure blue, one pure brown, and two 
hybrid browns; and these two latter hybrids, under strictly 
analogous conditions, will in turn produce offspring in the 
ratio of 25 per cent pure blues to 25 per cent pure browns, 
to 50 per cent hybrid browns. 

So regular and definite are these relations and sequences 
that they have been formulated into a law known as Mendel's 
law. The principles that this law states have been used 
very extensively by horticulturalists, and by experimental 
biologists; these experimentations have brought forth the 
development of a great number of remarkable varieties, in 
both the animal and vegetable fields. Reasoning from the 
vast amount of data thus acquired, biologists of the Mende- 
lian school see in the segregation of the gametes a logical 
explanation for the origin of species ; and they explain progress 
by assuming a natural persistence of those forms best adapted 
to cope with the exigencies of environment. 

Applying the Mendelian hypothesis to the illustrations 
opening this chapter, it may be assumed that the gametes 
of Elizabeth Edwards possessed dominants manifested in 
intellectual capacity; those of the Lee and Randolph families 
included dominants eventuating in political and military 
leadership ; while those of the Jukes had dominants pertaining 
to the more primitive sensibilities, the later-evolved charac- 
teristics correlated with higher attributes being with them 
absent or deeply recessive. That higher dominants may be 
present with lower recessives is indicated in the fact that the 
zygotes from the union of Richard Edwards with his second 
wife produced offspring of relative mediocrity. Whereas 
Elizabeth Tuttle had furnished the dominants so superlative 
as to keep recedent Edwards' recessives, apparently his 
second wife furnished superlative recessives which uniting 


with gametes of a like quality made thence forth recedent 
some of Edwards' former dominants. The bearing of all 
this on the new study of Eugenics must be apparent to all 
thinking people. By an appropriate linking of the right 
gametes, poor stock may be increasingly limited and good 
stock correspondingly increased. Thus by utilizing natural 
principles, our offspring may be more strongly endowed; then, 
by applying psychological principles of education, that 
endowment may be developed to limits as yet unknown. 

However, let no one think the process is simple. Deter- 
minants do not exist singly, but in hundreds of thousands; 
unit characters are not passed on independently, but together 
in loose or firm aggregations; moreover, determinants seem 
to exert some influence one on the other, somewhat after the 
fashion suggested by Weissman, with the possibility of 
multitudinous complications. 


Thomson: Heredity, 1908. 
Conklin: Heredity and Environment, 1914. 
Morgan: The Physical Basis of Heredity, 1919, 
Conn: Social Evolution and Social Heredity, 1914. 
Castle: Genetics and Eugenics. 
Newnan: Evolution, Genetics and Eugenics. 
Kellogg: Mind and Heredity. 
Huntington: Civilization and Climate. 

Morgan: Education and Heredity, Yale Review for July, 1924. 
Jennings: Heredity and Environment, Scientific Monthly, Septemiber, 


Acromion — the point of the shoulder. 
Anlage — the earhest anatomical foreshadowing. 
Analgesic— giving relief from pain. 
Antigenic — capable of producing antibodies. 

Antithrombin — the substance in the blood that prevents clotting. 
Arborization— the branching termination of a nerve-cell process. 
Autonomic— self -controlling. 

Atjtacoid— producing a substance that is elsewhere effective. 
AuTRUSiON— reaching out toward. 

Axon— that process of a nerve-cell that conducts impulses from the 


Biuret Reaction — a specific test for detecting the presence of proteins. 
Bolus — a rounded mass. 

Castration— excision of the male sexual gland. 

Caudad— toward the tail end of the body. 

Cephal AD— toward the head end of the body. 

Cephalic— pertaining to the head. 

Chalone— a substance that exerts an inhibitory effect elsewhere. 

Chemotropism— dynamic influence exerted on cells by chemical force. 

Chromaffin— pertaining to tissues akin to the adrenal gland. 

Commensurate— at about the same level. 

Commissural— joining corresponding parts. 

Conjugate Unilaterality— coupled so that two lateral sides seem as 

Corpus Lutem — the yellow tissue in the cortex of the ovary succeeding 

a discharged ovum. 
Cortex — the surface layer of an organ or part. 
CoRTiciFUGAL — proceeding away from the cortex. 
Corticipetal — proceeding toward the corte:^. 



Deglutition— swallowing. 

Dendrites — those processes of a nerve-cell that from other sources 

receive impulses and conduct them into the cell-body. 
Diastole — the dilation phase of the heart's action. 

Ectodermal — the outer layer of the primitive embryo. 

Embryogenesis — the development of the embryo. 

Emunctory— concerned with excretion. 

Endoderm — the inner layer of the primitive embryo. 

Endogenous — produced within. 

Endometrial — pertaining to the endometrium. 

Endometrium — the mucous membrane that lines the cavity of the 

EpiCRiTic^pertaining to the power of perceiving fine variations. 
Exogenous — produced from without. 

Fasciculum— pertaining to an extended grouping or column of fibers. 
Faucial— relating to the passage from the mouth to the throat. 
Fibrinogen — that substance in the blood from which fibrin is derived. 
Fovea Centralis — the retinal area of most discriminating vision. 


Gamete — a sexual cell after reduction of the chromosomes. 

Glycemia — sugar in the blood. 

Glycogenesis — the formation of the liver sugar glycogen. 

Glycogenolysis — the breaking down of glycogen into blood-sugar. 

Glycolysis— the breaking down of sugar. 

Glycophysis— the taking up of sugar from the blood by the tissues. 

Glycosuria— the presence of sugar in the urine. 

Gonad — an essential sexual gland; the ovary or the testicle. 

Gynecology — a study of the diseases peculiar to women. 


Hallucination — an abnormal perception misconceived as having an 
objective reality. 


Helicotrema — the small passage at the apex of the cochlea whereby 

the scala tympani connects with the scala vestibuU. 
Hemic— pertaining to the blood. 
Hepatic— pertaining to the liver. 

Hermaphroditic— appearing to possess the attributes of both sexes. 
Heterolateral — having reference to the opposite sides. 
Histology— pertaining to the microscopic structure of tissue. 
Homogeneous — of uniform quaUty. 
Homolateral — having reference to the same side. 
Homologous — of similar structure, function^ or location. 
Hormone — a substance that chemically stimulates activity elsewhere. 
Hypermetropia — far-sightedness. 


Illusion — a wrong interpretation of a sensory excitation. 
Integration — the assimilation of numerous factors for the production 

of something more complex. 
Internuncial— that which associates correlated neural activities. 
Interstitial — pertaining to that which occupies intermediate areas. 


Kinase — that which serves to activate some enzyme. 

Labile— that which is unstable. 

Lactogenic — that which serves to induce a flow of milk. 


Menopause— referring to that age in life when the menstrual flow 

Mesad— in a direction more toward the middle line. 
Mnemonics — pertaining to the phenomena of the memory process. 
Modality— a characteristic quality. 

Molar — pertaining to mass as distinguished from molecular. 
Morphogenetic — that which serves to produce form or shape. 
Myometrium— the muscle substance of the uterus. 
Myelenation — the formation of a sheath about a nerve fiber. 
Mydriasis— undue dilatation of the pupil. 
Myopia — near-sightedness. 
Myosis— undue contraction of the pupil. 


Occlusion— the state of being closed. 
Oophorectomy— the excision of an ovary. 
Opercular — that which serves as a cover. 


Parturition — the process of giving birth. 

Peristalsis — the progressing contraction of the longitudinal muscles 

of a tubular structure whereby the contents are moved on. 
Petrosa — that portion of the temporal bone housing the organs of 

Phylogenetic — development of an organism according to the species 

Precestrum — preceding the period in animals when impregnation is 

Projicient — the projecting of a sensation to its physical source. 
Proprioceptive— pertaining to that which occurs within the body. 
Proteolysis — the breaking into simpler forms of protein food. 
Protopathic — primitive reaction, especially one that wards off danger. 


RoLANDic Area — that part of the cerebral cortex intimately concerned 
with the sending out of messages to the voluntary muscles. 


Sapid — that which can be tasted. 

Secretogogue— that which causes a secretion to flow. 

SoMESTHETic— pertaining to body feelings. 

Spay — to remove the ovaries. 

Stomatodeum — that portion of the ectoderm from which are formed 

the mouth and pharjmx. 
Stroma — the framework tissue of an organ. 
Synchronous — occurring at the same time. 
Systole — the contraction phase of the heart's activity. 

Tachycardia— undue rapidity of heart action. 
Tectal— referring to the roof of the mesencephalon. 
Tegmentum— an area of the brain underlying the thalamus. 
Testicle — the essential male gland for reproduction. 
Tonicity— referring to a state of continual mild tension. 
Toxemia — absorption into the blood of bacterial poisons. 

Vegetative— concerned with the functions of growth and nutrition. 
Ventrad — toward the abdominal aspect. 

Zygote — the living organism resulting from the union of a male and a 
female gamete. 



Absorption in the large intestine, 

in the small intestine, 44 

in the stomach, 40 
Acapnia, 130 

Accelerations of the heart, 94 
Accessories of diet, 166 
Accommodation reflex, 263 
Acromegaly, 279 
Addison's disease, 296 
Adrenin, 294, 295 
Alcohol, 67 
Amino-acids, 43. 47 
Amino-bodies, 54, 72 
Amylase, 43 
Anoxaemia, 130 
Appetite, 230^ 
Artificial respiration, 132 
Astigmatism, 266 
Auditory center, 214 

sensations, 234 
Auricles, 80 
Autonomic antagonisms, 203 

system. 195 


Basal ganglia, 189 
Beriberi, 62 
Bile, 48 

pigments, 50 

salts, 49 
Binocular vision, 281 
Bladder, 76 
Bhnd spot, 270 
Blood, constituents of, 110 

flow, rate of, 98 

physiolog\' of, 109 

Blood platelets, 113 
pressure, 99 
quantity of, 109 
red corpuscles of. 111 
specific gravity of, 109 
white corpuscles of, 113 

Body temperature, 135 

Breath sounds, 132 

Caffeine, 67 

Calcium, 61 

Canals of Schlemm, 266, 286 

Capillary pressure, 100 

Carbohydrate metabolism, 57, 59 

Carbon dioxide in the blood, 127 

Cardiac cycle, 81 

nerves, 94 
Cardio-inhibitory center, 94 
Caudate nucleus, 189 
Cell, 17 

Cerebellum, 156, 184 
Cerebral peduncles, 184 
Cerebrum, 211 
Chalones, 300 
Chemical changes in respiration, 

Chemistry of muscle, 25 
Cholesterol, 50 
Chromatic aberration, 261 
Ciliated cells, 28 
Circulation of blood, 99 
Coagulation of blood, 113 
Coffee, 67 
Cold spots, 145 
Color blindness, 276 
tests for, 278 

contrast, 280 

vision, 271 



Conjugated sulphates, 48, 73 
Conjunctiva, 286 
Consciousness, 224 
Contractility, 21 
Contraction of the pupil, 261 

wave of the heart, 91 
Convoluted tubules, 74 
Coronary arteries, 92 
Corporata striata, 189 
Corpus luteum, 306 
Corresponding points, 283 
Corti, organ of, 240 
Coughing, 132 
Creatin, 73 
Creatinin, 52, 73 
Cretinism, 297 

Darwin, 318 
Defecation, 47 
Deglutition, 32 
Depressor fibers, 106 

nerve, 96 
Determination of sex, 318 
Diabetes, 58, 232 
Diastole, 80 
Diastolic pressure, 180 
Dicrotic notch, 103 
Diencephalon, 154, 186 
Diet containing vitamines, 64 
Digestion in the large intestine, 47 

in the small intestine, 41 

in the stomach, 37 
Digestive system, 29 
Dilatation of the pupil, 263 
Diopters, 260 
Dreams, ^254 

Eighth nerve, cochlear division, 
vestibular division, 169 
Eleventh nerve, 178 
Elimination, 69 
Emotions, 227 

and the autonomic system, 206 
Enterokinase, 43 
Erepsin, 44 

Eruption of the teeth, 41 
Expiration, 123 
Eye, 256 

Faii point, 260 

sightedness, 265 
Fatigue of muscle, 24 
Fat metabolism, 59 
Fat-soluble A, 62 
Feces, 48 
Fibrin, 114 
Fifth nerve, motor division, 179 

sensory division, 183 
First nerve, 192 
Focusing, 259 

Food-containing vitamines, 64 
Force of heart action, 86 
Fourth nerve, 182 
Fovea, 286 

Gall-bladder, 49 
Gas changes in the tissues, 127 
Gases in the blood, 110 
Gastric activity, 34 

juice, 39 

peristalsis, 34 
Gigantism, 299 
Glaucoma, 286 
Glomerulus, 74 
Glossary, 323 
Glycogen, 31 
Glycogenesis, 57 
Glycogenolysis, 57 
Glycolysis, 58 
Glycophysis, 58 
Goiter, 298 
Gonads, 300 
Goose flesh, 139 
Growth of cell, 19 

Hallijcinations, 220 
Hearing, limits of, 265 
Heart, 78 

and inorganic salts, 90 

beat, time relations of, 82 
rate of, 84 

changes in form and position of, 

course of blood through, 79 

force of action of, 86 



Heart muscle, properties of, 8 

nerves, 94 

rate vs. blood pressure, 85 

sounds, 83 

valves, 80 
Heart's contraction wave, 91 

electrical condition, 97 

nutrition, 92 
Heat dissipation, 141 

loss from the body, 136 
regulation of, 138 

mechanism, control of, 139 

production, 135 
regulation of, 136 
Hemoglobin, 112 
Heredity, 218, 317 
Hering's theory of color, 275 
Hiccough, 133 
Hippuric acid, 173 
Hormones, 40, 287 
Hot spots, 145 
Hyperglossal nerve, 176 
H3TDerglycemia, 58 
Hypermetropia, 265 
Hypnoidal states, 226 
Hvpophysis, 269 
Hunger, 229 

Illusion, 220 
Immunity, 115 
Inhibitors of the heart, 94 
Inorganic salts, 61 
Insalivation, 31 
Inspiration, 122 
Insulin, 58, 294 
Internal secretions, 287 
Interstitial cells, 301 
Intestinal activity, 40 
Intracardiac pressure, 87 
Intravascular pressure, 266, 286 
Intrathoracic pressure, 124 
Invertase, 41 
Iris, 262 
Iron, 61 

Irritability of a cell, 18 
of a muscle, 22 

Labyrinth, 250 
lAictaso, 44 

Lamarck, 318 

Langerhans, islands of, 52 

Larynx, 252 

Lens, 258 

Light reflex, 262 

Lipase, 44 

Liver, 48 

Locke's solution, 90 

Lumbar autonomics, 200 

Lymph, 116 - 


Macula lutea, 268 
Maltase, 44 

Mammary gland, 300, 314 
Mastication, 29 
Maturation, 306 
Maturity, 305 
Medulla, 167 
Mendelian theory, 319 
Menstruation, 305 
Mv^.ntality vs. autonomies, 207 
Mesencephalic autonomics, 195 
Mesencephalon, 180 
Metabolism, 54, 66 

of cell, 18 
Motion of a cell, 18 
Motor sDeech, 213 
Muscle, ^21 

conditions affecting, 23 

contraction, theories of, 26 

work of. 27 
Maturation, 319 
Myogenic theory, 71 
Myopia, 264 
Mvxdedema, 298 


Near point of vision, 260 
Near-sightedness, 264 
Nervous system, 147 
Neurogenic theory, 91 
Ninth, nerve, motor division, 176 

sensory division, 169 
Nitrogen in the blood, 127 
Nourishment of the embryo, 310 
Nuclease, 44 
Nutritive condition of musclo, 23 



Old-sightedness, 265 
Olfactory nerve, 193 
Oncometer, 107 
Optic nerve, 192 
thalamus, 186 
Ovulation, 306 
Oxidations, 137 
Oxygen in the blood, 127 

Pain, 144 

Pancreatic secretion, 42, .52 

Pangenesis, 348 

Parathyroids, 296 

Parturition, 313 

Pepsin, 37 

Perception, 219 

Peristalsis, 40 

Perspiration, 141 

Physical changes in respiration, 125 

Pineal body, 188 

Pitch, 253 

Pituitary body, 188, 299 

Plasma of blood, 110 

Plethysmograph, 107 

Pleura, 133 

Plexuses of Auerbach and Meissner, 

Polypeptids, 43 
Potassium, 61 
Posterior longitudinal fasciculus, 

Presbyopia, 205 
Pressor fibers, 106 
Projection of auditory sensations, 

Prosencephalon, 154 
Protease, 43 
Protein, daily requirement of, 55 

metabolism, 57 
Proteins of the blood, 111 

essential, 56 
Ptyalin, 32 
Pulse pressure, 100 

wave, 102 

velocity of, 102 
Purin bodies, 32 
Pyloric control, 37 
P;^rramidal tracts, 165 


QuADRiGEMiNATE bodies, 180 


Rate of heart beat,. 82 
Red blood corpuscles. 111 

nucleus, 181 
Reproduction, 303 

of a cell, 19 
Respiration, 119 
Respiratory activity, 129 

center, 178 

quotient, 127 
Retina, 266 
Rhodopsin, 268 
Rickets, 62 
Rubro-spinal tract, 166 

i Saccule, 249 
Sacral autonomics, 200 
Schematic eye, 257 
Scurvy, 63 
Secondary sexual characteristics, 

Second nerve. 162 
Secretion, 43 
Secretogogues, 39 
Segmental contractions, 40 
Semicircular canals, 247 
I Sensation, 217 
I Seventh nerve, motor division, 180 

sensory division, 169 
Shivering, 141 
Sighing, 137 
Sixth nerve, 180 
Size of image, 260 
Skin, 157 
Sleep, 222 
Smell, 232 

center, 214 
Sneezing, 132 
Snoring, 133 
Sobbing, 133 
Sodium, 61, 74 
Sounds of the heart, 83 
Speech, 255 
Spherical aberration, 261 



Sphygmogram, 102 
Spinal cord, 157 

conduction in, 163 

reflexes, 209 
Splanchnic autonomics, 199 
Spleen, 52 
Striate body, 189 
Succus entericus, 44 
Sulphates, inorganic, 73 

organic, 73 
Systole, 80 
Systolic pressure, 100 

Table of autonomic functions, 205 
Taste, 231 

center, 214 
Teeth, eruption of, 31 
Temperature of the body, 135 

sense, 145 
Tenth nerve, motor division, 177 

sensory division, 169 
Thalamus, 186 
Third nerve, 181 
Thirst, 230 
Thrombin, 114 
Thymus, 297 
Thyroid, 297 
Timbre, 254 
Tonicity, 23 
Touch, 142 
Trance states, 226 
Trochlear nerve, 182 
Trypsin, 43 
Trypsinogen, 43 

Urates, 72 
Urea, 52, 72 
Ureters, 76 
Urethra, 77 
Uric acid, 74 


Urine, 69 

constituents of, 71 
secretion of, 74 

Utricle, 249 

Vagus nerve, 169 
Valves of the heart, 80 
Variations in blood-pressure, 100 
Vascular system, 84 
Vaso-constrictor center 
Vasomotor apparatus, 
of, 107 

nerves, 104 

supply, 107 
Venae ca^^ae, 79 
Venous pulse, 104 
Ventricles of the heart. 
Vesicular murmur, 132 
Vestibulo-spinal tract, 166 
Vision, 256 

center of, 214 
Visual judgments, 284 
Vitamines, 62 

table of, 64 
Vocal cords, 252 
Voice, 252 



Waier-soluble B, 62 
Weissman, 318 

Xanthins, 72 


Yawning, 173 
Young-Helmholtz theory, 274 

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